Genetics Test Biology

Ayache

Genotype ratio for two trait cross

9 DD, 3 DR, 3RD, 1RR

Phenotype ratio for two trait cross

15 dominant traits, 1 recessive trait

Sex-linked genes

the gene is located on the x chromosome

examples of sex-linked problems

hemophilia, color blindness, muscular dystrophy, male pattern baldness

what is hemophilia

bleeders disease

Mendel’s main contribution

independent assortment

what is independent assortment

the discovery that during meiosis, alleles segregate and do so independent of how the other pairs sort (each gamete contains only one factor from each pair of factors)

Single dominance

the dominant allele completely masks the recessive allele

incomplete dominance

when one allele doesn’t completely mask the other, the result is a blend of something in between

examples of incomplete dominance

red flowers crossing with white flowers and producing pink flowers, hair type, sickle cell trait

codominance

both alleles expressing themselves completely, neither allele completely masking the other (result is a little of each)

multiple alleles

3 or more alleles coding for a trait

blood typing

some traits have 3 or more alleles for a trait but you only inherit 2 of them

blood types

type a: aa, ao; type b: bb, bo; type o: oo; type ab: ab (ab is an example of codominance)

examples of multiple alleles

blood typing alleles and eye color

polygenetic traits

multiple genes influencing the trait (3 or more)

polygenetic inheritance pattern with examples

each trait has two alleles so if the trait is influenced by 2 genes, that means 4 alleles, 3 genes=6 alleles, etc. a polygenic trail can also be influenced by genes with multiple alleles

examples of polygenetic traits

hair color, eye color, skin color, height

phenotype

physical characteristics

genotype

genetic makeup (homozygous dominant, heterozygous or homozygous recessive)

allele

form of a gene, a trait is controlled by 2 alleles

test cross

the method to try and find out if the gene’s genotype is homozygous dominant or heterozygous, use punnet squares and examine the possible genotypes of the offspring with both pgeneration genotypes

pgeneration

parents

f1

children

f2

grandchildren

carriers

heterozygous individuals who have the recessive trait but because they are not homozygous recessive, do not show the trait. Carriers can pass the gene on to other generations

autosome

any chromosome that is not a sex chromosome

autosomal dominant v. autosomal recessive

if the dominant allele is present, disease is present; no dominant alleles can be present for the disease to not appear (two recessive alleles)

pleiotropy

inheritance pattern in which one gene affects many phenotype characteristics of the individual

example of pleiotropy

marfan syndrome

why is sickle cell anemia an example of pleiotropy

the tendency of sickle red blood cells to break down can damage the body

recessive or dominant: hemophilia

recessive

recessive or dominant: color blindness

recessive

recessive or dominant: male pattern baldness

recessive

recessive or dominant: muscular dystrophy

recessive

Pedigree Charts

visual diagrams that map out family history and relationships across generations

how can pedigree charts be used to determine genotype

tracking traits across family lines allow you to determine the genotypes of individual people and how the generations can pass down traits

zygote

a fertilized egg

how are zygotes related to fertilizations

zygotes are made when a female egg cell is fertilized by a male sperm cell, resulting in a diploid cell with half the fathers chromosomes and half the mothers

example of law of independent assortment

pea plant example where Mendel tracked seed color and seed shape of pea plants and instead of seeing the original parental combinations it created four completely independent gamate types (9:3:3:1 ratio)

mendel’s law of segregation

each organism has two alleles when these alleles segregate during mitosis to form gametes, each offspring only inherits one allele from each parent in order to maintain the pair

how Mendel’s law of segregation relates to a dihybrid cross

dihybrid crosses are the inheritance of two different genes so due to the law of segregation each pair separates and it is applied to each gene separately. This makes the cross be (for example) RrYy x RrYy