Designer Genes Division C

Principals of Genetics

gene

a unit of inheritance that usually is directly responsible for one trait or character. Each individual has two genes for each trait, one comes from dad and the other from mom

alleles

alternate forms of a gene. Usually there are two alleles for every gene, sometimes there are more than two alleles present in population – termed multiple alleles

homozygous

when the two alleles are the same

heterozygous

when the two alleles are different

genotype

the gene makeup of an organism. Phenotype is the trait of an individual expresses while genotype is the two genes that cause that trait

phenotype

the physical expression of the genes for the trait by an individual

Sex-linked Dominant

dominant gene on a sex chromosome

Sex-linked Recessive

recessive gene on a sex chromosome

Monohybrid Cross

● Hybrid – Ss X Ss

● One Trait – Smooth vs wrinkled

● Two gametes per parent

● S and s

● Punnett Square with 4 boxes – 4 offspring

Genotype frequency 1:2:1 Phenotype frequency 3:1

Dihybrid Cross –

Dihybrid – 2 traits

Gametes per parent = 4

Punnett Square – 16 boxes

Genotype ratio 1:2:1:2:4:2:1:2:1 Phenotype ratio 9:3:3:1

Incomplete Dominance

one allele (gene) is not completely dominant over another resulting in a blending of traits and where the phenotype of a hybrid displays a blending of the two alleles

-Hybrid

Genotype frequency 1:2:1

Phenotype frequency 1:2:1

Codominance

co-dominance – both dominant alleles (genes) in an individual are expressed as in blood types

(Know genotypes and phenotypes of this)

Independent Assortment

genes on different chromosomes separate independently during meiosis

Linkage

genes on the same chromosome are inherited as a group

Sex linkage

– allele (gene) is located on a sex chromosome and it will be more common in one sex

It is usually on the x-chromosome and more common in males than in females.

● Barr bodies – tightly coiled X chromosome in females – inactive X chromosome.

● Calico cats – usually on females. yellow and black alleles on X chromosome - female has 2 X’s

Genetic Variations

Probability – ratios or percents

Multiple Alleles – three or more alleles for a gene as blood type as skin color Multifactorial Traits – more than 1 pair of genes plus environment

Pleiotrophy – the action of an allele (gene) affects many parts of the body as sickle cell anemia

Variable expressivity – an allele (gene) can be expressed differently in different people

Environmental influence on genes expression

● Gene function is influenced by environment as with identical twins

● Genes have blueprint for proteins or parts of proteins

● Proteins can be structural proteins (parts of body) or functional proteins (hormones/enzymes