unit 5

mendelian inheritance

traits coded for by one gene w/ two alleles, where one allele is fully dominant over the other

law of segregation

genes on different chromosomes must segregate equally into gametes

each gamete receives one gene copy

homozygous

organism inherited two identical alleles at the same gene

heterozygous

organism inherited two different alleles at the same gene

genotype

organisms underlying genetic make-up consisting of both physically visible & non-expressed alleles

phenotype

the observable traits expressed by an organism

• physical traits

monohybrid cross

two organisms differing in one trait

law of independent assortment

alleles for different traits are inherited independently of one and other during the formation of gametes

karyotype

visual rep of an organisms chromosomes

down syndrome

triploidy 21

triple X syndrome

XXX (three x chromosomes)

klinefelters syndrome

XXY

males are born with an extra X

turners syndrome

X

jacobs syndrome

XYY

males born with an extra Y

autosomal recessive inheritance pattern

autosomal dominant inheritance pattern

codominance

both alleles for the same characteristic are simultaneously expressed in the heterozygote

incomplete dominance

expression of two contrasting alleles such that the heterozygous individual displays an intermediate phenotype

• blending of alleles is expressed

multiple alleles

single trait controlled by more than two alleles

ex- blood type (A, B, AB, O)

polygenetics

single trait is controlled by more than one gene

• seen in traits with a “sliding scale” → hair color, eye color, weight, height

• often influenced by environmental factors

• epistasis

epistasis

one gene masks/ interferes with the expression of another

ex- black and brown mice

pleiotropy

expression of multiple traits by a single gene

• occurs because genes code for proteins, and proteins themselves perform functions

non-nuclear inheritance

female gametes in animals and plants contain the majority of cellular component inherited by the zygote

• this is because male gametes are are small and only contain nucleus & cytoplasm

mitochondrial & chloroplast DNA is

exclusively maternal

linked genes

genes inherited together because they are nearby and on the same chromosome

• result: genes are rarely separated by crossing over & random assortment

• do not follow expected ratios (alternative hypothesis)

• recombination frequency of <50%

map distance

how close together 2 genes are, determined by crossing over frequency

ex- pair of genes have a recombination frequency of 10%, so they are 10 map units apart

sex-linked genes

traits determined by genes located on sex chromosomes

• most of these traits are coded for on the X chromosome since its bigger

Y-linked chromosomes

all males of a family will express the trait, no females

X-linked genes (female)

operate the same way as Mendelian traits

carriers

carriers

heterozygous individual who carries a recessive gene but doesn't express it

X-linked genes (males)

will only express the dominant or recessive trait

• cant be heterozygous

• hemizygotes

hemizygote

having only one allele for a trait

X-linked recessive

more males are effected than females, males cannot inherit the trait from their fathers

X-linked dominant

affected fathers pass on trait to all daughters

phenotypic plasticity

more than one phenotype can be expressed from one genotype, depending on gene expression & environmental conditions

prophase I

• chromatin condenses into chromosomes

• homologous pair up

• nuclear envelope dissolves

• spindle fibers form from centrosomes & attach to the kinetochores at the chromosomes

  • each homologous chromosome attached to fibers from opposite poles

• homologous chromosomes pair up and undergo recombination

  • synapse allows this to happen

• 4 different chromosomes result

  • 2 recombinant, 2 non-recombinant

locus (loci)

location of a gene on a chromosome

recombinant

recombination of genetic material

crossing over (recombination) happens at ___

chiasma/chiasmata

metaphase I

• homologous pairs line up along the center of the cell

  • either chromosomes of the pair may face either side of the cell

  • this gives more genetic variation

anaphase I

• spindle fibers pull homologous pairs apart

  • no longer identical sister chromatids stay tg

• spindle fibers must pull each pair to opposite side & break the synapse

  • goes wrong = nondisjunction

nondisjunction pattern in anaphase I

n+1, n+1, n-1, n-1

nondisjunction

wrong number of chromosomes in each daughter cell

telophase I

• meiotic spindle breaks down

• nuclear envelope reappears to fully separate the homologous pairs

  • each nucleus contains a haploid # of chromosomes

• chromosomes uncoil into chromatin

cytokinesis

cleavage furrow/ cell plate forms to full separate animal cells

meiosis I creates ___

2 haploid cells from 1 diploid cell

prophase II

• chromatin condenses into chromosomes + nuclear envelope breaks down

• new spindle fibers form

metaphase II

• non-identical sister chromatids line up at the center of the cell

• each chromatid is attached to a spindle fiber from opposite poles of the cell

anaphase II

• non-identical sister chromatids are pulled to opposite poles of the cell be shortening spindle fibers

  • goes wrong = nondisjunction

telophase II

• chromosomes uncoil into chromatid

• nuclear envelope forms around each haploid set of single chromatid DNA

  • all genetically unique

• meitotic machinery breaks down

cytokinesis II

4 genetically unique haploid cells are formed

null hypothesis

there is no relation/ difference between two groups of data

independent variable has no effect on dependent variable

alternative hypothesis

observed results are due to non-random cause

null hypothesis in genetic problems

there is no relation between genes (they are unlinked and randomly assorted)

rejecting the null hypothesis

• when the critical value is lower than the chi-squared value

  • “if the p is low, reject that ho”

• means that genes are linked

failing to reject the null hypothesis

• when the critical value is higher than the chi-squared value

• means that there is no significant difference in the data, results are due to chance

  • insufficient evidence to prove linkage

degrees of freedom

number of distinct possible values minus 1