Semester 2 Flashcards
(92 cards)
1
Q
Most characteristics are inherited from…
A
Parents
2
Q
Genetic information that is passed on from one generation to the next is found in …
A
DNA molecules
3
Q
DNA stands for
A
Deoxyribose Nucleic Acid
4
Q
DNA is classed as
A
macromolecule called nucleic acids
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Q
DNA is divided into thousands of shorted segments called
A
genes
6
Q
what do genes code for
A
the production of proteins
7
Q
DNA molecules are found inside your cells, packaged as
A
Chromosomes
8
Q
Nucleotides
A
a polymer, al long molecule made of monomers (building blocks)
9
Q
Make up of a nucleotide
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nitrogen containing base, deoxyribose sugar, phosphate molecule
10
Q
How are the nucleotides linked together
A
linked together along each strand (of DNA, DNA is a double-stranded molecule) by the phosphate of one joining to the sugar of another, forming a sugar-phosphate backbone
11
Q
The bases of opposing DNA strands are joined via
A
hydrogen bonds (weak bond)
12
Q
Double stranded DNA forms a
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double helix shape, with strands running anti-parallel (run upside down to one another)
13
Q
Four different nitrogenous bases
A
Adenine (A) Thymine (T) Guanine (G) Cytosine (C)
14
Q
complementary base pairing
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Adenine can only pair up with Thymine: A – T
Guanine can only pair up with Cytosine: G – C
15
Q
Genome
A
collection of genes in a cell, the sum total of an organisms’ DNA in one haploid cell
16
Q
Genes are units of
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hereditary information
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Q
DNA is made up of
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genes and non-coding regions
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Q
coding region of each gene comprises of
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a sequence of three nucleotide subsegments called triplets, these provide instructions for a cell to assemble amino-acids into a polypeptide chain, the basic structure of a protein
19
Q
Types of proteins
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Structural, Enzymes, Signaling, Regulatory, Transport, Sensory, Motor, Defense, Storage
20
Q
Structural proteins function
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strengthen cells, tissues, organs and more
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Q
Enzymes function
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Build and break down molecules, critical for growth, digestion and many other processes in the cell, without enzymes, chemical reactions would happen too slowly to sustain life
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Q
Signaling proteins function
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allow cells to communicate with each other, signals, receptors, and relay proteins work together to get information from the outside of the cell to the inside
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Q
Regulatory proteins function
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bind to DNA to turn genes on and off
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Q
Transport proteins function
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move molecules and nutrients around the body and in and out of cells
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Sensory proteins function
help us learn about are environment, help us detect light, sound, touch, smell, taste, pain and heat
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Motor proteins function
keep cells moving and changing shape, also transport components around inside cells
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Defense proteins function
help fight infection, heal damaged tissue, and evade predators
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Storage proteins function
store nutrients and energy-rich molecules for later use
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Alleles
different variation of the same gene
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Loci
position of a chromosome
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Haploid cell
cell that contains a single set of chromosomes, half the number of chromosomes typically found in most cells of an organism.
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Diploid cell
A diploid cell is a type of cell that contains two sets of chromosomes. diploid cells have one set of chromosomes from each parent, resulting in a total of 46 chromosomes in each diploid cell
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Homologous Chromosomes
pair of chromosomes that are similar in size, shape, and genetic content, are of the same length and centromere location, and they have the same genes at the same loci
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Chromsome
a structure that packages a single DNA molecule and its associated proteins in a cell, Each chromosome contains a set of genes, which are passed on to daughter cells when a cell replicates.
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DNA in Prokaryotes
single circular chromosome located in the nucleoid, may also contain small fragments of DNA called plasmids
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DNA in Eukaryotes
the majority of DNA is found in the nucleus in linear form and is called nuclear DNA
The way that DNA exists inside the nucleus of eukaryotic cells depends on the stage of the cell cycle.
Interphase: DNA will be long, thin strands
Cell division: DNA condenses into shortened, thicker structures, recognized as chromosomes
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DNA during the cell division process
DNA is very long and thins, so for it to be moved around a cell during cell division processes, it must be packaged efficiently
It is coiled and supercoiled upon itself, around proteins called histones
DNA wrapped around 8 histones is called a nucleosome
Chromosome only become visible as recognizable structure after DNA replication
The centromere acts as a connection between two copies (the original strand and the new strand), called sister chromatids
Different chromosomes have their centromeres in different positions
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A single unreplicated chromosome has two arms the..
the shorter arm is the p arm
the linger arm is the q arm
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spacer
Not all parts of a chromosome are genes. In between each gene is a region called a spacer. These regions of DNA do not code for a protein.
One of the purposes of spacers is to separate the genes to make it easier for other molecules to interact with them
The size of a chromosome is thus determined by the number of genes and the amount of spacer DNA
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classification of chromosomes depends on
- Size
- Position of centromere
- Sex determining or not
- Gene position/banding pattern
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Autosomes
chromosomes not involved in sex determination
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Allosomes
are the sex-determining chromosomes, X and Y
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Homogametic
Sex chromosomes for human females are homologous, as the X chromosomes have the same genes, this state is called homogametic
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Heterogametic
Sex chromosomes for males are non-homologous, since the X and Y chromosomes have different genes. This state is called heterogametic
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Ploidy level of a cell
number of chromosomes sets it carries
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Gametes
reproductive cells (sperm in males and eggs in females) that have half the usual number of chromosomes, contain only one set of chromosomes (haploid (n) )
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Somatic cells
any cells in the body of an organism except for reproductive cells (gametes). contain two sets of chromosomes, one from each parent - diploid (2n)
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Karyotype
visual representation of the complete set of chromosomes in an individual's cells, arranged in pairs according to their size, shape, and banding patterns. Homologues are arranged according to banding patterns, centromere positions and size
They are then ordered from 1 -22 from the largest chromosome (1) to the smallest (22), with the sex chromosomes at the end
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Aneuploidy
when the cells of an organism vary in the usual number of chromosomes by having one extra or one fewer chromosomes
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trisomy
If an organism's cells have one extra chromosome
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monosomy
If an organism's cells have one fewer chromosome
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Turner syndrome karyotype
Turner syndrome X O, only one X chromosome and no Y
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Polyploidy
is a chromosomal abnormality in which an organism has more than two complete sets of chromosomes
Three sets is termed triploid
Four sets is termed tetraploid
Polyploids is lethal in humans but is tolerated in many plants
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Gametes
sperm cells and egg cells (ova)
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Germ line cells
the cells that give rise to gametes, found in the gonads
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gonads
testes and ovaries
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sperm and egg cell genetic material
Sperm and egg cells only have half the genetic material that normal somatic cells have, so are known as haploid (n).
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Meiosis
How these germ cells produce the gametes is by a type of cell division called meiosis, which occurs in the gonads.
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Fertilization occurs when
Fertilization occurs when the haploid gametes fuse to form a diploid zygote i.e. the first cell of the new individual.
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Why is meiosis known as a reduction division
Meiosis is known as a reduction division because it reduces the number of chromosomes in the daughter cells to half (n) that of somatic cells (2n).
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Two stages of meiosis
Meiosis occurs in two stages, ending up with 4 genetically unique daughter cells:
* Meiosis I: homologous chromosome pairs separate
* Meiosis II: chromatids separate
In each of the stages of division, cells go through four phases: prophase, metaphase, anaphase, and telophase.
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DNA replication occurs when
DNA replication occurs in the S phase of interphase, prior to meiosis.
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Prophase 1
Chromosomes condense and appear as homologous pairs, crossing over occurs late in this phase
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Metaphase 1
Homologous chromosomes line up on metaphase plate and attach to the meitotic spindle
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Anaphase 1
Homologous chromosomes separate and move to opposite poles. chromosomes are till double stranded - Still made of 2 chromatids centromeres do not separate
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Telophase 1
Cleavage furrow appears nuclear envelope beings to form 2 haploid daughter cells result
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Cytokinesis
nuclear envelope forms 2 haploid daughter cells result
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Prophase II
In both daughter cells nuclear envelope breaks down chromosomes condense spindles begin forming
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Metaphase II
In both daughter cells, chromosomes arrange on the central metaphase plate attached to spindle
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Anaphase II
Centromere separates
sister chromatids (now single-stranded chromosomes) move to opposite poles of the two daughter cells
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Telophase II
Cleavage furrow appears, nuclear envelope forms
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Cytokinesis
cleavage furrow separates daughter cells 4 haploid daughter cells result
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Crossing - over
During synapsis (in Prophase 1), crossing-over occurs. This involves breaks in the DNA, called chiasmata (sing. chiasma). Non-sister chromatids bind at the point of the break.
Non-sister chromatids then exchange DNA, including one or more genes.
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chiasmata
breaks in the DNA, There may be many chiasmata between two homologues.
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Recombination
The resulting chromosomes after crossing over are recombinant chromosomes and have new combinations of alleles i.e. recombination has occurred. This increases genetic diversity.
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Independent Assortment
During Metaphase I, when the chromosome pairs align along the equator of the cell, the orientation of each pair is completely random.
The chromosomes then separate and move to opposite poles, resulting in a random assortment of chromosomes in each gamete.
This is known as independent assortment, which increases genetic diversity.
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What increases genetic diversity throughout meiosis?
independent assortment
recombination
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Spermatogenesis
gamete formation for males
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oogenesis
gamete formation for females
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Mitosis vs Meiosis
Mitosis
Genetic recombination - no
Number of parent cells - 1
Number of chromosomes in parent cell - 2n
Number of daughter cells/identical or unique - 2 identical
Number of chromosomes in daughter cell - 2n (diploid)
Meiosis
Genetic recombination - yes
Number of parent cells - 1
Number of chromosomes in parent cell - 2n
Number of daughter cells/ identical or unique - 4 unique
Number of chromosomes in daughter cell - n (haploid)
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Dominant allele
If one allele or trait overrides another, it is referred to as dominant.
This dominance is represented by using a capital letter for the allele.
A dominant trait will be expressed whether the genotype is heterozygous or homozygous.
Only one copy of the dominant allele is needed for the corresponding trait to be expressed.
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Recessive allele
If an allele is only expressed when it is in a homozygous genotype, it is referred to as recessive. Therefore, two copies of the allele are required for the corresponding trait to be expressed.
Recessive alleles are only expressed when no dominant allele is present. The recessive trait is overridden by the dominant trait in the heterozygous genotype.
Recessive alleles are represented by a lowercase letter.
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Genotype
The genotype of an organism refers to its genetic make-up.
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Phenotype
The phenotype of an organism refers to its observable features or traits, determined by both genotype and environment.
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If a gene on an autosomal chromosome has two alleles, there are three different combinations that could be inherited. E.g. the gene for petal colour:
Homozygous dominant – PP
Homozygous recessive – pp
Heterozygous – Pp
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Homozygous
genotype has the same allele, sometimes referred to as pure breeding
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Heterozygous
genotype has different alleles, also referred to as hybrid.
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Codominance
When both alleles are fully expressed in the phenotype of a heterozygote, they are described as codominant.
Neither allele masks the expression of the other allele.
For the genotypes, a standard capital letter stays the same, with two different superscript letters to represent the two different alleles.
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Multiple alleles
A gene may have more than two alleles - a multiple allele system.
The four common blood groups of the human ABO blood group system – A, B, AB, and O - are determined by three alleles: IA, IB, IO/i.
The IA and IB alleles are co-dominant. They code for enzymes that join sugars together on the surface of red blood cells.
IO produces a non-functional enzyme.
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Incomplete dominance
When neither allele is fully expressed in the phenotype of a heterozygote and the resulting trait is a blending of both alleles, it is a situation of incomplete dominance.
The phenotype of the heterozygote is a different trait to that observed in either homozygote.
□ E.g. crossing red and white gives pink.
For the genotypes, a standard capital letter stays the same, with two different superscript letters to represent the two different alleles.
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Sex linkage
Females have two X chromosomes and males have an X chromosome and a Y chromosome.
Sex-linked genes are present on either the X or Y chromosomes.
The X chromosome is larger with about 900 genes, which are referred to as X-linked.
The Y chromosome has about 100 genes, which code for Y-linked traits in males.
X-linked traits are more likely to be expressed in males because alleles on the one X chromosome they inherit from their mothers have no corresponding alleles on the Y chromosome they receive from their fathers. Whether the allele is dominant or recessive, it is expressed in the phenotype.
Males pass X-linked trait
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X-linked genotypes
X-linked alleles are written as superscripts on the letter X e.g. XA or Xa.
As females have two copies of the X chromosome, they can be homozygous or heterozygous.
However, as males only have one copy of the X chromosome, they are referred to as hemizygous.
