Probability and Inheritance of traits

Homozygous dominate

RR

Hetrozygous

Rr

Homozygous recessive

rr

Phenotypic ratios

dominate:recessive

Geneotypic ratios

non-carrier:carrier:suffers:

If affected individual are in every generation with no skipping and affected individuals have affected parent. They are likely?

dominate

If skipping occurs, and/or affected individuals have both parents unaffected. They are likely?

recessive

A trait is Y linked if?

Only boys are affected, boy must have an affected dad and all sons of an affected male are affected

A trait is X linked if?

Affected male have an affected mom, and all daughters are affected

Law of dominance

• one allele may be dominant, and the other recessive.

• The dominant allele determines the trait that is expressed in the phenotype, while the recessive allele is masked in the presence of the dominant allele.

Law of segregation 

• Each individual has two alleles for each trait, one inherited from each parent. During gamete formation, these alleles segregate so that each gamete carries only one allele for each trait.

Law of Independent Assortment

• According to this law, the alleles for different traits segregate independently of each other during gamete formation.

monohybrid cross 

• A genetic experiment that involves the study of the inheritance of a single trait. 

• Organisms that differ in only one characteristic are crossed to understand how that specific trait is passed from one generation to the next.

Dihybrid Crosses:

• A genetic experiment that involves the study of the inheritance of two different traits simultaneously. 

• Organisms that differ in two characteristics are crossed to understand how these traits are passed from one generation to the next

Ratio for 2 hetero parents 

1 homozygous dominant : 2 heterozygous : 1 homozygous recessive

Ratio for hetero and homo recessive parent

1 heterozygous: 1 homzygous recessive

Test cross

• used to determine the genotype of an individual expressing a dominant phenotype. By mating with a homozygous recessive individual

Ratio for hetero dihybrid

9 dominant phenotype:  3 look dominant for one trait and recessive for other:  3 look recessive for one trait and dominant for the other:  1 homozygous recessive for both traits

epistatic 

Genes that interfere with the expression of other genes

Pleiotropic Alleles 

• When a single allele can affect several traits at the same time.

Chromosome Theory

Chromosomes carry genes (units of heredity)

2.   Paired chromosomes segregate during meiosis (producing haploid cells)

3.   Chromosomes assort independently

4.   Each chromosome contains many different genes

Autosomal dominate 

• present in each generation

• Affected individuals, on average, transmit the disorder to 50% of offspring

• Males and females are equally affected

• Cannot have carriers

Autosomal Recessive

• Disorder may skip a generation

• Affected offspring generally have normal (but heterozygous) parents

• male and female are equally affected 

X-Linked Dominant

• observed in each generation

• Mothers pass trait on to both sexes

• Fathers pass trait only to daughters

• No carriers

X-Linked Recessive

• Affect males more than females

• No transmission from father to son

• Daughters of affected males are carriers

• Carrier Females pass affected allele onto ½ sons

• Affected females have affected fathers and carrier mothers

Y-Linked Disorders

• Always passed down from father to son.

• All sons are affected in every generation

• Y chromosome doesn’t have many genes

  • Male infertility

Gene linkage

 tendency of certain genes to be inherited together because they are located on the same chromosome.

Conjugation

• A form of sexual reproduction in which genetic material is switched between two bacterial cells.

codominance

two different alleles for a gene are expressed equally and fully in an organism's phenotype