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Flashcards in Genetics Deck (89)
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1

Genes

-DNA sequences that code for heritable traits that can be passed from one generation to the next
-determine physical and chemical characteristics of every human

2

Alleles

-alternative forms of each gene
-cell holds two of these -- one from mom and one from dad

3

Genotype

genetic combination possessed by an individual (ex. TT, tt, Tt)

4

Phenotype

the manifestation of a given genotype as an observable trait

5

Homologues

-two copies of each chromosome (ex. XX)
-expressed by each human except for males who have XY

6

Chromosome

-genes are organized into these
-ensure that genetic material is passed easily to each daughter cell during meiosis and mitosis
-each one of these is part of a homologous pair

7

How many alleles does each person inherit for each gene?

two alleles for all genes except for male sex chromosomes (XY)

8

Dominant Allele

-only one copy of an allele is needed to express a given phenotype
-usually expressed with a capital letter

9

Recessive Allele

-two copies of the allele are needed to express a given phenotype
-usually represented with a lowercase letter

10

Hemizygous Genotype

describes a situation in which only one allele is present for a given gene, as is the case for parts of the X chromosome in men

11

Complete Dominance

-when only one dominant and one recessive allele exist for a given gene
-presence of one dominant allele will mask the presence of the recessive allele

12

Codominance

-when more than one dominant allele exists for a given gene
-Ex. person with one allele for A blood antigen and one allele for B blood antigen will express both antigens simultaneously

13

Incomplete Dominance

-when a heterozygote expresses a phenotype that is intermediate between the two homozygous genotypes
-Ex. when a red flower is crossed with a white flower and it results in pink flowers

14

Penetrance

-the frequency that a genotype will show up in a phenotype
-the proportion of the population with a given genotype who actually express the phenotype
-considered a population parameter

15

Full Penetrance

-occurs when 100% of individuals with a given genotype express the phenotype
-Ex. if you have the gene for being smart then there is a 100% chance you will be smart

16

High Penetrance

occurs when most, but not all, of those with the allele show the given phenotype

17

Expressivity

-to what degree a gene is expressed
-the different manifestations of the same genotype across the population
-defined as varying phenotypes despite identical genotypes
-commonly considered at the individual level

18

Constant Expressivity

all individuals with a given genotype express the same phenotype

19

Variable Expressivity

individuals with the same genotype may have different phenotypes

20

Mendel's First Law of Segregation

-genes exist in alternative forms (alleles)
-an organism has two alleles for each gene, one inherited from each parent
-two alleles segregate during meiosis resulting in gametes that carry only one allele for any inherited trait
-if two alleles of an organism are different, only one will be fully expressed and the other will be silent (codominance and incomplete dominance are exceptions to this)

21

What is the key cellular correlate of Mendele's First Law?

separation of homologous chromosomes during anaphase 1 of meiosis

22

Mendel's Second Law of Independent Assortment

-states that the inheritance of one gene does not affect the inheritance of another gene
-exhibited during prophase I of meiosis when homologous chromosomes pair up to form tetrads and swapping of genetic material between chromatids can occur (recombination) which ultimately allows the inheritance of one gene to be independent of others

23

____ and ____ ____ allow for greater genetic diversity in the offspring

-segregation
-independent assortment

24

Gene Pool

all of the alleles that exist within a species

25

Mutation

change in the DNA sequence that results in a mutant allele

26

Wild-Type

alleles that are considered "normal" or "natural" and are ubiquitous in the population

27

Mutagens

-substances that cause mutations
-all carcinogens are these

28

Transposons

-can lead to mutations
-elements that can insert and removed themselves from the genome
-if it is inserted in the middle of a coding sequence, the mutation will disrupt the gene

29

What are the different nucleotide-level mutations that occur?

-point mutations (silent mutations, missense mutations, nonsense mutations)
-frameshift mutations

30

Point Mutations

-occur when one nucleotide in DNA (A, C, T, G) is swapped for another
-includes silent, missense, and nonsense mutations