Topic 3 - Genetics

Question 1

DNA

Answer 1

a polymer made up of two strands coiled to form a double helix. strands linked by a series of complementary base pairs joined together by weak hydrogen bonds. made up of nucleotides that consist of a sugar and phosphate group with one of the four different bases attatched to the sugar

Question 2

chromosome

Answer 2

a large DNA molecule made into a small package by tightly coiling DNA around a protein

Question 3

DNA structure

Answer 3

a polymer made from many nucleotides
two strands going in opposite directions
each strand held together by weak hydrogen bonds
double helix
complementary base pairs
sugar-phosphate backbone

Question 4

DNA bases

Answer 4

Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)

Question 5

complementary base pairs

Answer 5

A pairs with T
C pairs with G

Question 6

hydrogen bonds

Answer 6

weak force holding the two strands of DNA together

Question 7

allele

Answer 7

different version of the same gene. We have two alleles of each gene

Question 8

homozygous

Answer 8

two copies of the same allele

Question 9

heterozygous

Answer 9

two different copies of the same allele

Question 10

dominant

Answer 10

one copy needed for characteristic to show. written as capital

Question 11

recessive

Answer 11

two copies needed for characteristic to show. written as lowercase

Question 12

genotype

Answer 12

combination of alleles in an organism (genetic make-up)

Question 13

phenotype

Answer 13

characteristics produced by the alleles

Question 14

steps and reasons of DNA extraction

Answer 14

1. cut fruit/plant into chunks and mash as much as possible - mashing helps break apart cells from one another & break open cells (increases the surface area)
2. make extraction buffer using water, salt, detergent then stir together with mashed fruit - detergent: protease dissolves/breaks down proteins in the cell membrane and salt makes the DNA stick together. destroys enzymes that may break down the DNA
3. incubate the mixture at 60°C for 15 minutes - high temperature breaks down cell wall exposing membranes
4. filter the mixture using a sieve so you can just have the liquid - the DNA can be found in the liquid
5. slowly pour ice cold ethanol down the side of the test tube/beaker and leave to settle - ethanol: DNA cannot dissolve in alcohol so precipitates it out.

Question 15

mutation

Answer 15

a rare, random/spontaneous change to the genetic material (bases) in a gene that can be inherited

Question 16

Human Genome Project (HGP)

Answer 16

project involving many scientists from many countries to find the order of bases in human DNA

Question 17

how is the HGP useful?

Answer 17

to tailer drugs to genes, to design better drugs

Question 18

goals of the HGP

Answer 18

to decode the sequence of DNA bases
to identify and interpret all the genes in the human DNA

Question 19

outcomes of the HGP

Answer 19

• sequenced the order of the bases in the human genome
• could develop new, specific/personalised medicines and drugs
• map and find genes
• find amino acid sequences
• help identify mutations

Question 20

entire cost of the HGP

Answer 20

$3 billion

Question 21

genetic variation

Answer 21

natural differences between members of a species caused by genes

Question 22

gametes

Answer 22

sex cells (egg and sperm)

Question 23

fertilisation

Answer 23

sperm cell fuses with egg cell and nuclei combine

Question 24

zygote

Answer 24

single cell formed by fertilisation

Question 25

gene

Answer 25

a section of a DNA molecule that codes for a specific protein. controls characteristics

Question 26

genome

Answer 26

the entire DNA of an organism

Question 27

diploid

Answer 27

cells with 23 pairs of chromosomes (46 in total)

Question 28

haploid

Answer 28

cells with 23 single chromosomes

Question 29

meiosis

Answer 29

a type of cell division to form gametes (sex cells)

Question 30

meiosis features of process

Answer 30

chromosomes duplicate before division begins 1 duplication stage 2 cell divisions new cells are haploid there is genetic variation in the cells formed (genetically different) 4 cells produced PRODUCT: 4 genetically different haploid daughter cell

Question 31

roles of meiosis

Answer 31

gamete formation for sexual reproduction enables genetic diversity

Question 32

deoxyribose

Answer 32

the pentose sugar found in DNA

Question 33

what is the arrangement of complementary polynucleotides in the double helix?

Answer 33

antiparallel

Question 34

nucleotide

Answer 34

monomer of nucleic acids like DNA

Question 35

most phenotypic features are as a result of multiple genes rather than single gene inheritance

Question 36

key facts for mutations and variation

Answer 36

- most genetic mutations have no effect on the phenotype - some mutations have a small effect on the phenotype - rarely, a single genetic mutation will significantly affect the phenotype - there is usually extensive genetic variation within a population of a species and these arise through mutations

Question 37

change in DNA code (mutation) > different amino acid used > different protein made > phenotype looks different

Question 38

continuous variation

Answer 38

There is a graduation between one extreme and another of a given characteristic. Measured on a numerical scale e.g. height and weight

Question 39

discontinuous variation

Answer 39

A characteristic is either present or absent and there are no intermediate forms. It is in discrete groups or categories e.g. human blood groups, fingerprints, tongue rolling

Question 40

Explain how variation is caused (5 marks)

Answer 40

Reference to: - Variation is difference between organisms - Variation can be due to your genes - Due to mutation - Due to meiosis forming different gametes - Gametes fusing / fertilisation - Combining of genetic material during fertilisation - Dominant or recessive alleles - Environmental variation e.g diet, sunlight exposure, physical activity - Acquired characteristics e.g scars

Question 41

Why do alleles lead to differences in inherited characteristics?

Answer 41

because different alleles code for different forms of the same protein

Question 42

Causes of variation that influence phenotype

Answer 42

- genetic variation: different characteristics as a result of mutation and sexual reproduction - environmental variation: different characteristics caused by an organism's environment (acquired characteristics)

Question 43

there is usually extensive genetic variation within in a population of a species and that these arise through mutations

Question 44

most genetic mutations have no effect on the phenotype some mutations have a small effect on the phenotype rarely does a single mutation will significantly affect the phenotype