Ch9: Genes and Inheritance

heredity

-the passing of characteristics from parent to offspring through the parent’s genes

-your mother and father contribute to your genetic makeup

parents and children

the passing of genes can often be seen when comparing _______ and _______

selective breeding

the passing of genes can be manipulated or controlled by ______________

23 pairs

humans have _______ of chromosomes, one maternal copy and one paternal copy

alleles

we inherit 2 copies of each gene, even though there are different versions called ______

one; multiple

-some traits are controlled by just ___ gene (ex: fur length in cats)

-but most are influenced by ______ genes and the environment

Gregor Mendel

-a monk

-Father of genetics

-studied garden peas

-Mendel’s experiments (cross breeding colored flowers)

Mendel’s Observations

-when he crossed true breeding purple flower plants with true breeding white flower plants, the next generation had ALL PURPLE flowers

-when he crossed these 2nd generation plants, they had mostly purple flower plants, but some were white flowered

true-breeding

plants that always produce offspring with the same trait as the parent

Mendel’s Confusion

-how did offspring have traits that parents didn’t?

-dominant trait masks the effect of a recessive trait when an individual carried both the dominant and recessive version of a trait

-dominant (what you see)

-recessive (what you don’t see)

Mendel’s Conclusion & Rule of Heredity

-each parent puts a single set of genes in each sperm or egg it makes

-each offspring inherits one copy of the trait from each parent

-for a total of 2 copies of the instructions for any trait

-observed trait: depends on the 2 copies of the gene it inherits from its parents

phenotype

the outward appearance and behavior of an individual (ex: a albino deer has little or no pigment on their body)

genotype

an organism’s genetic composition for a particular trait (ex: homozygous for the recessive allele for albinism deer)

recessive alleles

___________ can be masked by alleles in heterozygous individuals

homozygous genotype

when an organism inherits the same allele from each parent

heterozygous genotype

inheriting a different allele from each parent

Mendel’s Law of Segregation

-each parent passes along an instruction set for a particular trait called a gene

-because of Law of Segregation, generation 2 plants were heterozygous because they inherited different allele from each parent (one purple & one white)

punnett squares

used to predict genotype outcomes from a cross

genetic outcomes

segregation and fertilization are chance events, which use probability to predict certain ___________ from the genotypes of parents

testcross

mates an individual that has the recessive genotype with an individual with unknown genotype

pedigrees

-we use these to decipher and predict the inheritance patterns of genes

-when you know the alleles an individual carries, this may be used to determine whether a trait is: dominant or recessive, sex linked (carried on X or Y chromosome), or autosomal (carried on non-sex chromosome)

females; males

in pedigrees, circles are the symbols for ________, and squares are the symbols for ______

trait

in pedigrees, filled in shapes tell us that a certain organisms exhibits the ____ of interest

incomplete dominance

the phenotype of a heterozygote is intermediate between the phenotypes of the two homozygotes

(ex: blue + yellow = green)

codominance

a heterozygous individual shows both alleles

(ex: people that have AB blood type)

multiple alleles

some genes have more than two alleles

antigens

like signposts in the body’s immune system, and they help identify “self” vs “non-self”

ex: organ transplants

antibodies

immune system molecules in bloodstream that attack foreign invaders

blood compatibility: type A

donates to: Type A and Type AB

receives from: Type A and Type O

blood compatibility: type B

donates to: Type B and Type AB

receives from: Type B and Type O

blood compatibility: type AB

donates to: Type AB

receives from: all four types

“universal recipient”

blood compatibility: type O

donates to: all four types

receives from: Type O

“universal donor”

Rh markers

-individuals with one or two copies of the dominant Rh cell surface marker (“Rh positive”)

-individuals with two copies of recessive allele (“Rh negative”)

cannot

Rh-negative ______ receive Rh-positive blood

yes!

are Rh-positive individuals compatible with both Rh markers?

polygenic traits

-influenced by many different genes and are continuously varying traits (ex: height)

-many human behavioral traits are this

additive effect

when the effects of multiple genes contribute to the ultimate phenotype

pleiotropy

occurs when one gene influences multiple, unrelated traits; one gene with many effects

sex-linked traits

-differ in their patterns of expression in males and females

-red green color blindness is X-linked in humans

Mendel’s Law of Independent Assortment

when neither of two traits influences the inheritance of the other trait, it is said they are inherited independently of each other

dihybrid

an individual who is heterozygous for two traits

linked genes

when genes are close together, on the same chromosome, they are sometimes inherited together

ex: red hair + freckles