Genetics Exam 1 practice

Sex-linked

gene is on a sex chromosome

ex. red-green color blindness and hemophilia

Sex-influenced

gene expression differs between males and females.

Sex-limited

trait is expressed only in one sex

Genic sex-determination

genotypes at one or more loci determine the sex of an organism

X-linked characteristics

Trait’s caused by genes on the X(sex) chromosome

Nondisjunction

When cells fail to separate in anaphase 1 of meiosis

Lyon hypothesis

The hypothesis that in Female organisms, only 1 X will be activated

incomplete dominance

the heterozygote has an intermediate or blended phenotype

Codominance

both phenotypes are expressed together.

Penetrance

Asks whether the trait appears at all. If a trait has 80% penetrance, then 80% of individuals with the genotype show the phenotype, while 20% do not

Expressivity

asks how strongly or in what form the trait appears. Two people may both show the trait, but one may have a mild form and the other a severe form

epistatic gene

gene that does the masking

hypostatic gene

the gene being masked

Dominance

alleles of one gene interact

Epistasis

two different genes interact.

ratio 9:3:4 meaning?

usually indicates recessive epistasis. The last two classes are combined:

9 : 3 : (3 + 1)

ratio 12:3:1 meaning?

usually indicates dominant epistasis. The first two classes are combined:

(9 + 3) : 3 : 1

ratio 9:7 meaning?

often means that both genes are needed together to produce the main phenotype. The last three classes are combined:

9 : (3 + 3 + 1)

lethal alleles

A lethal allele causes death in a specific genotype. It does not always mean every individual carrying the allele dies.

multiple alleles

the typical is 2 alleles for a gene; a population can have more than two allele versions.

ex. For example, the ABO blood group has three common alleles in the population:

IA, IB, and i

But one person can only have two of them, such as I^AI^B, I^Ai, or ii.

Cytoplasmic inheritance

the genes are outside the nucleus, usually in mitochondria or chloroplasts. In humans, mitochondrial DNA is usually inherited from the mother because the egg contributes most of the cytoplasm.

Genetic maternal effect

The genes are nuclear genes, but the offspring’s phenotype is determined by the mother’s genotype. This happens because the mother places gene products such as RNA or proteins into the egg before fertilization.

Polygenic trait

many genes affect one trait

Pleiotropy

one gene affects many traits

Locus

Alleles of a specific gene found at a specific place on a chromosome

Genotype

refers to the overall set of alleles an organism has

monohybrid cross

a cross between two parents that tracks a singular inherited trait

Dihybrid cross

2 differing characteristics in parents

Principle of Segregation

A diploid organism has 2 alleles for a trait from the mother & father.

Independent assortment

2 alleles at a locus separate independently of alleles at other loci; homologous chromosomes separate independently (anaphase 1)

cohesin

holds sister chromatids together

separase

the molecular knife that cuts cohesin during anaphase

shugoshin

The glue that protects or acts as a protective layer for cohesin

why are oocytes, ovums, or meiosis products in general different when the cycle is done?

due to crossing over which occurs in prophase I and independent assortment

What shape is DNA?

Rod-shaped

What is Crossing over?

is the exchange of genetic material between nonsister chromatids ; occurs in prophase 1 of meiosis

Chromosome theory of heredity

Genes are found on chromosomes

Principle of Segregation

each diploid organism possesses 2 alleles at a locus that separate in meiosis, and 1 allele passes into each gamete

testcross

recessive epistasis

Characteristics of dominance

1. result of gene interaction at same locus

2. does not alter or change how genes are inherited

3. the type depends on level exhibited

→ Dominance is an allelic interaction

incomplete penetrance

the genotype does not always produce the expressed phenotype

gene interaction

genes at different loci interact to determine a single phenotype

phenocopies

How can I determine if a new mutation that is either Y linked or autosomal dominant?

By crossing a normal with an affected