bio ch 12
Terms
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copy deck
- linkage
- inheriteance of certain genes as a group because they are on the same chromosome
- crossing over
-
-occurs during prophase I of meiosis(cell division producing sex cells)
-exchange of corresponding segments of DNA between 2 homologous (same size & shape) chromosomes
-this produces new combinations of alleles on the 2 chromosomes - alleles
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one of several forms of a gene for a particular charateristic
ex. eye color: blue, green, brown, hazel - Genetic recombination
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new combination of alleles
help with survival of the species - Human Chromosomes
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Diploid #=46 (in body cells)
Haploid #=23 (in gametes)
23 pairs of chromosomes:
-22 pairs of autosomes
~body (somatic) chromo.
~same in both sexes
~homologous pairs
-1 pair of sex chromosomes
~determines gender & other characteristics
~Female (XX) Male (XY) - sex-linked characteristics
- characteristics that are determined by genes that are on only one type of sex chromosome, but not on the other
- X Chromosome
-
has many genes(approxiametly 1000)-some help determine female reproductive ability, gender
-also determines:
~color vision
~structural problems with muscles
~blood clotting factors - Y Chromosome
- has a few genes (78-80)-many of which determine gender and reproductive ability
- A few traits are sex-linked on the Y chromosome...
- they may only be expressed if there is no corresponding allele on the X chromosome
- Most traits are sex-linked on the X chromosome...
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Females-have 2 X chromosomes, so if genes are heterozygous (different), then the dominant allele is expressed.
Males-have only 1 X chromosome, so if that chromosome has a defective gene, there is no corresponding allele on the Y to counteract it, & the defectve trait will be expressed - Thomas Hunt Morgan
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-discovered sex linkage by studying eye color in Drosophila (fruit flies)
red eyes-dominant white eyes-recessive
-when Morgan crossed red eyed male and female:offspring:red eyes
-next generation cross produced: females-all red eyes
males-1/2 R, 1/2 W eyes
--no corresponding allele for red eyes on Y chromosome
He concluded that-W eyes are sex-linked on X chromo. - Incomplete dominance
- a pattern of inheritance where the heterozygous phenotype (Aa) is an intermediate between the two homozygous phenotypes(AA or aa)
- What is the cause of incomplete dominance?
-
usually due to genes that code for proteins with different abilities
ex. flowers: pink color is a phenotypic intermediate
Red + white = pink
RR R1R1 RR1
ex. human: wavy hair is a phenotypic intermediate
curly + straight = wavy
HH H1H1 HH1 - Multiple Alleles
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in a given species there may be many different alleles for every trait, even though any given individual organism of the species may only have two alleles for that trait (1 from each parent).
-different alleles arise due to mutations - Example of multiple alleles: Blood types
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3 diff. alleles - A, B, o
A & B=dominant
o=recessive - Codominance
- both alleles are expressed equally both alleles are dominant
- polygenic inheritance
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the interactino of two or more genes contributes to a single phenotype
ex. in humans- eye color, skin color, hair color, ear shape - Pleiotropy
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a single gene influences more than one phenotypic trait
ex. SRY gene-codes for androgen receptor protein-activates genes for many male sex characteristics
ex. Marfan sydrome=heart defects, eye defects, connective tissue defects - Environmental Influence on Gene Expression
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*temp-influences fur color in rabbits. enzyme that produces black fur(pigment) is inactive above 93 F- so only colder parts are black
*exposure to UV rays-changes skin color
*lack of nutrients-alter height, alter health, IQ - pedigree
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diagram showing genetic relationships among family members over several generations
-help determine if genes are: sex linked, dominant or recessive, if person is heterozygous or homozygous - Albinism
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ex. of recessive genetic disorder
caused by a mutant TYR gene. TYR codes for the enzyme tyrosinase-enzyme which is needed to make melanin
-light skin and hair, lack of eye color pigment (red because blood vessels show) - Hemochromatosis
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most commmone recessive genetic disorder in US (1/10 are carriers)
-intestines take away too much iron and put it in waste - Sickle-Cell Anemia
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ex. of recessive genetic disorder
caused by mutation in one of the genes(alpha chain or beta chain) that produces hemoglobin-more commone in blacks
-nucleotide substitutioncauses wrong amino acid to be placed in the hemoglobin polypeptide chain, causing amino acid molecules to clump together-mishapen RBC
-sickled cells are delicate, they dont carry O2, clog capillaries, cause pain, anemia
-heterozygotes have 1 normal allele for hemoglobin so they are ok-some have normal RBC
-homozygotes(hh)-have no normal RBC *resistance to malaria* - Cystic Fibrosis
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ex. of recessive genetic disorder
many diff. mutations of the CTFR gene may cause CF. mutation causes chloride pumps (protiens) to work improperly, or not at all, so Cl- can't move to airway surfaces. H20 typically follows Cl-, but does not move well in people w/CF. So, H20 can't dilate the mucus->builds up in lungs & digestive tract
-heterozygotes usually have enough functioning Cl- pumps so secretions in lungs have more H20 so mucus is not as thick
*Americans, Canadieans, Europeans* - Tay-Sachs
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ex. of recessive genetic disorder
rapid neurological deterioration at a young age
*Eastern European Jews* - Marfan Syndrome
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ex. of dominant genetic disorder
caused by one mutant allele that codes for the protein fibrillin
-mutant form of fibrillin protein stimulates extra bone growth and weakens connective tissue
-long arm and leg bones, weak heart valves and arteris
-Lincoln may have had Marfan - fibrillin
- long fibrous proteins found in tendons, ligaments, artery walls, heart valves
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Achondroplasia
Polydactyly
Hyperchloesterolemia
Huntington Disease -
ex. of dominant genetic disorder
dwarfism
extra fingers, toes
high blood cholesterol
degenerative neurological disorder(doesn't show up until age 30) - Sex-linked genetic disorders
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sex-linked on X chromosome have a unique pattern of inheritance- son gets X-chromosome only from mother, & son can pass it on to daughter
-Disorders sex-linked on X appear more freqyently in males because they only have 1 X-chromosome - Duchenne Muscular Dystrophy
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sex-linked on X chromosome
-recessive - Hemophilia
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caused by a mutation in an allele on X chromosome that codes for a blood clotting factor (protein)
-recessive
-bleeding (external/internal
-anemia
-bruising - - Factor VIII - Red-green Colorblindness
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sex-linked on X chromosome, so more males are colorblind
-inability to detect red/green - nondisjunction
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failure of homologous chromosomes to separate correctly during meiosis
*incidence of nondisjunction in eggs increases greatly after age 35
*more frequent in eggs because eggs have been there for awhile and sperm is on a need basis - What are the causes of errors in number of chromosomes
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-in meiosis I-if the 2 homologous pairs fail to separate during anaphase I: 4 abnormal gametes
-in meiosis II-if the 2 sister chromatids fail to separate: 2 normal gametes & 2 abnormal gametes - Karyotype
- photograph of stained chromosomes arranged largest to smallest
- Turner Syndrome
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Sperm(O)+Egg(X)=XO
Sperm(X)+Egg(O)=XO
-females with lack of secondary sex characteristics, lack of mature eggs, infertile, sometimes lower intelligence
-short, skin folds in neck= "webbed neck"
-increased chance of cardiovascular disease, kidney problems, hearing problems - Trisomy X (Triple X) (XXX)
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Sperm(XX)+Egg(X)=XXX
Sperm(X)+Egg(XX)=XXX
-sometimes taller, sometimes lower intelligence, fertile
*female - Klinefelter Syndrome
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Sperm(XY)+Egg(X)=XXY
Sperm(Y)+Egg(XX)=XXY
-Males, usually sterile(due to low sperm count), some show female traits(small breasts, broad hips), somtimes low intelligence - XYY Male
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Sperm(YY)+Egg(X)=XYY
-higher testosterone levels, acne, slightly lower IQ, very tall
-genetic predisposition to violence? PROBABLY NOT - Trisomy 21 (Down Syndrome)
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-mild to severe mental retardation, heart malformations, distinctive eyelid shape, poor immune resistance
-age of mother is a factor-incidence increased greatly after age 35-due to nondisjunction - Protooncogene
- inactive gene that has the potential to become an oncogene, if mutated
- oncogene
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gene that causes cancer
-if activated("turned on"=transcribed) it will: 1. speed up growth rate 2. decrease differeatiation - Tumor-suppressor gene (TSG)
- slows cell growth, promotes cell specialization-if "turned off"-not copied any more-abnormal cells may develop
- Retinoblastoma
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cancer of eye (growth on retina)
1st cancer proven to have a genetic link