Genetics Midterm 1 Vocabulary

true-breeding lines

a variety that produces the same trait across generations (pure bred)

single-factor cross

a cross in which an experimenter observes one character

monohybrids

Parents that are heterozygous for one character.

reciprocal cross

same outcome

Dominant

Appears in F1

Recessive

Trait that is hidden in F1

Alleles

Different forms of a gene

Can a gene have more than two more than two alleles in the alleles in the population? In an population? In an individual?individual?

Yes in a population

BUT no, an individual can only have two alleles for a given gene because they inherit one allele from each parent

laws of segregation

two alleles for each trait must separate when gametes are formed then reunite at random, one from each parent at fertilization

Punnent Square Method

can be used to predict outcome of a cross or self fertilization experiment

product rule of probability

The chance of two or more independent events occurring together

sum rule of probability

the probability that exclusive events will occur is equal to the sum of their individual probabilities

What is the probability that both A and B will occur?

product rule

What is the probability of A or B occurring?

sum rule

Homoezygous

Have 2 identical alleles; can be both dominant and both recessive

Heterozygous

An organism that has two different alleles for a trait

Genotype

genetic composition of an individual

Phenotype

Observable traits of an organism.

Test cross

a mating in which an individual showing the dominant phenotype (but unknown genotype Y-) is crossed with an individual with the recessive phenotype

dihybrid cross

A cross between individuals that have different alleles for the same gene

Results of Mendel's dihybrid cross F2

contained both parental types and recombinant types

Results of Mendel's dihybrid cross alleles

assort independently and appear in any combination in the offspring

law of independent assortment

during gamete formation, different pairs of alleles segregate independently of each other

monohybrid ratio

3:1

dihybrid ratio

9:3:3:1

Probability Formula

number of individuals with a given phenotype /total number of individuals

Loci Assort Independently

we can look at each locus independently to get the answer

heterozygous incross

binomial expansion equation

probability of an unordered combination of outcomes

Pedigrees

a chart that shows a trait in a family and how it is inherited

Symbols of a pedigree

-circle: female

-square: male

-shaded: trait present/affected by trait

-1/2 shaded: carrier of trait

-not shaded: not affected by trait

vertical pattern of inheritance indicates

rare dominant trait

vertical pattern pedigree trait example

huntington disease

Huntington's disease

a hereditary disease marked by degeneration of the brain cells and causing progressive dementia.

horizontal pattern of inheritance indicates

rare recessive trait

horizontal pattern of inheritance example

cystic fibrosis

cystic fibrosis

A genetic disorder that is present at birth and affects both the respiratory and digestive systems.

Key aspects of pedigrees with dominant traits

1. affected children have at least one affected parent

2. vertical pattern of inheritance

3. affected parents can produce unaffected children if both parents are heterozygotes

four aspects of pedigrees with recessive traits

1. affected individuals can be children of two unaffected parents

2. all children of affected parents should be affected

3. rare recessive traits show horizontal pattern

4. could show vertical pattern of inheritance if trait is common in the population

single gene inheritance

one gene may determine more than one trait

incomplete dominance

Cases in which one allele is not completely dominant over another

incomplete dominance example

flower Colour in snapdragons

phenotypic ratios are an ____ reflection of the genotypic ratios

exact

Codominance

F1 hybrids display traits of both parents

lentils offer an example of

multiple alleles

A 3:1 ratio in each cross indicates that....

different alleles of the same gene are involved

allele frequency

Number of times that an allele occurs in a gene pool compared with the number of alleles in that pool for the same gene

wild-type allele

most common allele in a population >1%

mutant allele

a rare allele in the same population <1%

monomorphic

a gene with only one common, wild-type allele

polymorphic

a gene with more than common

ABO blood types in humans are determined by...

three alleles of one gene

six genotypes produce ___ blood phenotypes

four

Gene I controls the type of

sugar polymer on surface of red blood cells

Human histocompatibility antigens

an extreme example of multiple alleles

three major genes encode

histocompatibility antigens

histocompatibility antigens gene has

400-1200 alleles each

sickle cell anemia

a genetic disorder that causes abnormal hemoglobin, resulting in some red blood cells assuming an abnormal sickle shape

how many alleles code for sickle cell anemia

multiple alleles, more than 400 so far

pleiotropy

A single gene having multiple effects on an individuals phenotype

HbBs allele

affects more than one trait

phenotype of heterozygote defines the

dominance relationship of two alleles

complete dominance

hybrid resembles one of the two parents

incomplete dominance

hybrid resembles neither parent

Ay allele

Dominant allele causing yellow coat color in mice, recessive lethal allele

Ay is dominant to A for

hair Colour

Ay is recessive to A for

lethality

2:1 ratio indicates

recessive lethal allele

pure breeding yellow (AyAy) mice

cannot be obtained because they are not viable

Pleiotropy

A single gene having multiple effects on an individuals phenotype that are distinct but seem unrelated

pleiotropy in humans

waardenburg syndrome

holt oram syndrome

Penetrance

The percentage of individuals with a particular genotype that shows the expected genotype.

penetrance can be

complete or incomplete

expressivity can be

variable or unvarying

Expressivity

the degree to which a trait is expressed

modifier genes

alter the phenotypes produced by alleles of other genes

modifier gene example

T locus of mice that causes short tails

environmental effects on phenotype #1

Temperature is a common element of the environment that can affect phenotype

coat Colour in siamese cats

phenocopy

A trait that appears inherited but is caused by the environment and not heritable

phenocopy example

phocomelia due to thalidomide

9:3:3:1 in F2

suggest two independently assorting genes for seed coat Colour

2 genes controlling the same trait

function additively in independent pathways

Epistasis

a gene interaction in which one gene mask the effect of another gene allele

epistatic allele

the allele that does the masking

hypostatic gene

gene that is masked

epistasis can be

recessive or dominant

recessive epistasis

9:3:4 ratio

recessive epistasis example

Labrador coat color (Yellow, brown, black)

Gene B determines

black or brown

recessive allele ee of gene E is epistatic to B and determines

yellow

genotype ee mask the effect of

all B genotypes

recessive epistasis in humans with rare blood ttype

bombay phenotype

homozygosity for the h bombay allele is epistatic to the l gene determining

ABO blood types

recessive epistasis in sweet peas

Purple F1 progeny are produced by crosses of two pure-breeding white lines

reciprocal recessive epistasis accounts for ____ flower in sweet peas

purple

Complementation

recessive allele is complemented by a wild type

dihybrid cross generates a ___ ratio in F2 progeny

9:7

reciprocal recessive epistasis

homozygosity for the recessive allele of either gene results in a white phenotype

Two genes work in tandem to produce purple sweet pea flowers

a dominant allele of each gene must be present to produce that color

heterogeneous traits

have the same phenotype but are caused by mutations in different genes