BIO test 3: principle of segregation, independent assortment, dominant vs. recessive, sex linked, pedigree

genetic variation

genetic differences that exist among individuals in a population at a particular point in time

genotype

the genetic makeup of a cell or organism

phenotype

an individual’s observable characteristics

• height, eye color, color blindness

• can be microscopic: insulin, bone density

homozygous

both alleles are the same in a genotype

heterozygous

the 2 alleles are different in a genotype

Gregor Mendel

father of genetics

• agustinian friar

• his experiments established the basic rules of heredity

• model organism was peas

model organism

a species that is used for research because it is practical to work with and the conclusions draw apply to many other species 

peas

the model organism used in Mendel’s experiments because of its easily classified traits with contrasting phenotypes

seven traits of peas

• seed color (green or yellow)

• seed shape (round or wrinkled)

• flower color (purple or white)

• pod color (green or yellow)

• flower position (axial or terminal)

• pod shape (smooth or indented)

• plant height (short or tall)

hybridization

mating or crossing between pairs of strains that differ in their phenotypes for 1 or 2 traits

true breeding

every offspring was identical to parents

• pure line

genes

what was the hereditary factor that Mendel hypothesized that was distinct for each of the observed pea plant phenotypes and the pea plant had two of?

artificial cross pollination 

1. anthers cut out of flowers

2. mature pollen collected from another flower and deposited on stigma of female

3. after fertilization, bagged to prevent any other pollen from entering

monohybrid cross

cross between two organism where there is only one differing trait between the two

parental generation

the starting generation that produce F1 generation

first fillial generation

the generation produced after the parent cross

T

dominant traits don’t necessarily improve fitness compared to recessive trait

Reciprocal crosses

a cross in which the phenotype of the male and female are reversed compound with a prior cross

• changing gender that contains certain gene

• Mendel found that gender did not affect these traits that masked the other

F1 generation

all had the same phenotype where the dominant gene and all the genotypes were heterozygous in mendel’s experiemnt

F2 generation

• self fertilization 

• 1 homozygous dominant: 2 heterozygous: 1 homozygous recessive

• 3 phenotype dominant: 1 phenotype recessive

principle of segregation

individuals inherit 2 copies of each gene, one from the mother and one from the father, and when individuals form reproductive cells, the 2 copies separate equally in the eggs and sperm

• eeach gamete carries only one allele for that trait

• the parent’s genotype is separated into gametes and the gametes contain 1 allele

• monohybrid cross

did not

mendel found that inheritance ____ work through blending

autosomal inheritance

the patterns of inheritance of any genes not on a sex chromosome.

• standard patterns of inheritance

gene

a hereditary factor that influences a particular trait

allele

a particular form of a gene 

domiant allele

an allele that produces its phenotype in heterozygous and homozygous genotypes

recessive allele

an allele that produces its phenotype only in homozygous genotypes

pure line

individuals of the same pheonotype that when crossed always produce offspring with the same phenotype

hybrid

offspring from crosses betwen homoxygous parentswith different genotypes

test cross

a cross of a homozygous recessive individual and an individual with the dominant phenotype but unknown genotype

statistical, probabilities

the principles of transmission genetics are ___ and can be stated as ____

0-1

the probability of any genotype must be between ___

principle of independent assortment

the 2 copies of each gene segregate into gametes independently of the 2 copies of another gene (dihybrid cross)

dihybrid cross

2 traits are crossed 

different, far apart, equally

genes assort independently because they are located on ___ chromosomes and are ___,and these chromosome have 2 ___ likely ways of lineing up before they are segregated

linked

but there is an exception to almost everything. If gene R and gene Y are close together on the same chromosome, they will likely not assort independently because they are ___

not

mendel’s law of independent assortment is ___ universal as law of segregation 

incomplete dominance

some genes have alleles that are neither fully dominant or fully recessive and an intermediate phenotype resluts

• Ex: pink flower

• heterozygous

codominance

2 alleles of a gene both produce their phenotypes in heterozygous

• ex: blood types

pleiothropic effect

a single gene can produce a protein that functions as many different parts of an organism

• ex: CFTR channel and cystic fibrosis

epistasis

the phenotypic expression of particular genotypes at one gene can be affected by the gene types present at the second gene

• 2 genes affect coat color in labrador retrievers

• gene interactions

X-linked traits

offspring have sex-dependent inheritance patterns

incomplete dominance

heterozygote displays both phenotypes at once

multiple alleles

hierachy of dominance

gene x environment

envvironment influences phenotype 

autosomes

In humans:

• chromosomes 1-22 are found in both females and males

homologous autosomes

same size, shape, and carry the same genes in the same order

sex chromosomes

chromosome 23, found in different combinations in males and females

• X and Y chromosomes

hemizygous

have half of the complement of genes because only have one set of genes on X-chromosomes, 

female

XX

male

XY

wildtype

common phenotype

mutants

individuals with an unusual phenotype due to a mutation 

• new allele!

Thomas Hunt Morgan

fruit fly guy who studied X-linked inheritance

• proposed that the gene for eye color in fruit flies is located on the X-chromosome and that the Y chromosome does not carry this gene

X linkage

a gene on the X-chromosome

Y linkage

a gene on the Y chromosome

horizontal line

what represents mating in pedigrees?

vertical line

what represents progeny/offspring in pedigrees?

oldest, youngest

progeny are arranged horizontally in birth order from to _

consanguineous mating

what does double lines indicate between relatives

increases

consanguineous mating___ genetic diseases and disorders

autosomal recessive

• individuals with the trait must be homozygous

• if the parent of an affected individual does not have the trait, then they must be heterozygous for the trait

• affect males and females equallly

• frequently observed as a result of consanguineous mating

carrier

heterozygous individuals who do not have an inherited disease but carry a recessive allele for it

cystic fibrosis

disease that affects the viscosity of body fluid

• autosomal recessive inheritance

• causes lung infections, transplants, and death

autosomal dominant

• males and females are equally likely to be affected

• affected offspring have at least one affected parent

• affected offspring are heterozygous if only one parent is affected

• affected individuals can be homozygous or heterozygous

• unaffected offspring are homozygous recessive

• if 1 parent is heterozygous, about half of offspring will be affected

• trait does not skip generation

huntington’s disease

removes cells in the brain; break down overtime

• autosomal dominant

males express the trait more often

how can you tell it is sex linked inheritance?

daughter

males can only transmit his X chromosome to his ___

mother

a male inherits his X-chromosome from his ___

X linked recessive inheritance

• males are affected more frequently than females

• trait is never passed father to son

• affected sons are usually born to carrier mothers

• about ½ sons of carrier mother will be affected

• all daughters of an affected male and unaffected non-carrier female are carriers

• trait often skips generations

hemophilia A

caused by a recessive mutation in the F8 gene on X chromosome

• females rarely affected because those who carry the mutation are likely heteroxygous (fathers pass only half, and the mother can pass off a chromosome that has the dominant allele)

X linked dominant

• males and femals are equally likely to be affected

• all daughters of an affected father are affected, but no sons

• affected sons always have affected mothers

• about ½ of the offspring of an affected mother are affected

• affected daughters can have an affected mother/father

• trait does not skip generations

• rare

aneploidy 

extra chromosomes

X chromosome

larger and contains more than 1000 genes

Y chromome

very small and contains about 50 genes

• almost none of the genes on the other chromomsome have counterparts on this chromosome

SRY

sex determining region Y, gene on the Y chromosme that ecodes a protein that activates the male sex determination pathway 

• aka “testes determining factor” bc it activates testes development in the embryo 

female

the default in human embryonic development is ___

mullerian duct

the frmale precursor to the fmale oviduct and uterus

wolffian duct

the precursor to the male seminiferous tubules, vas degerens, and epididymis

bipotential, sexually indifferent

here gonads are ___ and ____, meaning they either develop into ovaries or testes

development of testes

• SRY gene codes for protein to differentation of the testes

  • triggers path and shuts down female development pathway

• after testes are formed, they produce testosterone

• simultaneously, other pathways cause degradtion of precursors of the female internal reproductive organs

androgen receptor

protein receptor that binds to testosterone

X chromosome

where is the gene that codes for the androgen receptor (AR) located on?

blind, no effect

when the AR is missing or deffective, cells are ___ to tetosterone, and tetosterone will have ___ on sexual development because it is not perceived by the cells that should respond to it