chromosomes, mapping, and the meiosis-inheritance connection
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Chromosomes, Mapping, and the Meiosis-Inheritance Connection. Chapter 13. HUMAN GENETICS. Introduction 46 chromosomes in each cell (23 pairs) Autosomes: all chromosomes except sex chromosomes (22 pairs) Sex chromosomes: determine gender (1 pair). Sex determination XX = female - PowerPoint PPT PresentationTRANSCRIPT
Chromosomes, Mapping, and the Meiosis-Inheritance Connection
Chapter 13
HUMAN GENETICS
I. IntroductionA.46 chromosomes in each
cell (23 pairs)B.Autosomes: all
chromosomes except sex chromosomes (22 pairs)
C.Sex chromosomes: determine gender (1 pair)
1.Sex determinationa)XX = femaleb)XY = male
2.During meiosis, each egg from the female gets an X; 1/2 male sperm get X, 1/2 get Y
3.Males determine gender of offspring!a)Except in birds and reptiles
where female is XY and male is XX
II. Studying human geneticsA.Difficult because
1. Long generations (25 yrs)2. Single births3. Ethical concerns
B.Methods for studying humans1.Pedigrees: record that shows
how a trait is inherited within a family
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2. Population sampling1. Selecting a small # of people to
represent an entire population2. Must be a random sample3. Ex: through random sampling,
researchers discovered that 65% of people in US taste PTC, 35% cannot
3. Identical twin studiesa) Identical genetic codesb)Separated at birth: study which
traits are genetic(Nature) & which are environmental (Nurture)
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Human Genetic Disorders
Some human genetic disorders are caused by altered proteins.
the altered protein is encoded by a mutated DNA sequence
the altered protein does not function correctly, causing a change to the phenotype
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III. Inheritance of human traitsA. Dominant traits
1. Polydactyly - extra fingers & toes
2. Dwarfism - small size3. Curly hair4. Huntington disease - nervous
disorder5. Piebaldness - white patches of
hair
Vitiligo=AutoImmune
Piebaldness=Genetic
B.Recessive traits1.Straight hair2.Freckles3.Albino4.Cystic fibrosis - lung disorder5.Deafness6.PKU - nervous disorder
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Odds of having a child with the disease?
C.Codominance1.Sickle cell anemia - irregularly
shaped red blood cells• O allele = healthy(HH)• 1 allele = mild case(HS),
resistant to malaria• 2 alleles = severe case(SS)
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Sex Chromosomes
In each female cell, 1 X chromosome is inactivated and is highly condensed into a Barr body.
Females heterozygous for genes on the X chromosome are genetic mosaics.
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F. Sex-linked traits1. Genes located on X chromosome2. Males only have one X, so only
have one allele controlling these genes
3. Males more likely to have disorders that are sex-linked because they only need 1 recessive allele
4. Carrier: someone who has one allele for a disorder -- does not have the disease but can pass it on to children
5. Only women can be carriers for sex-linked traits
6. Examples: hemophilia, muscular dystrophy, colorblindness
Hemophilia in the Royal Families of Europe
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7. Color visiona)XC=Color Vision, Xc=colorblindb)Males - 8% colorblind (XcY)c) Females - 1% colorblind (XcXc)
Normal
Red-Green
Total
What are the chances for a healthy dad and a mom who is a carrier for colorblindness to have a child that
is colorblind?
IV. Genetic disordersA. Nondisjunction: failure of
chromosomes to separate during meiosis
1. Normal = 23 chromosomes2. Abnormal = 22 or 24
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3. Monosomy: too few chromosomes, one chromosome left unpaireda)Turner syndrome: female with
only 1 X chromosomeb)Short stature, sterile
4. Trisomy: too many chromosomes, extra copy of onea)Down’s syndrome: trisomy 21b)1 in 1400 when mother under age
25, 1 in 100 by age 40
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Human Genetic Disorders
Nondisjunction of sex chromosomes can result in:
XXX triple-X femalesXXY males (Klinefelter syndrome)XO females (Turner syndrome)OY nonviable zygotesXYY males (Jacob syndrome)
B.Detecting genetic disorders1. Physical characteristics - features,
disabilities2. Ultrasound - pictures of baby in
utero using sound waves3. Amniocentesis - sample of fluid from
around baby, can examine baby’s cells
http://www.biology.iupui.edu/biocourses/n100/2k4csomaldisordersnotes.html
http://www.katie.com/babyblog/archives/000538.html
http://www.katie.com/babyblog/archives/000538.html
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4.Karyotype: picture of a person’s cromosomes • taken from any cells -- blood
in adults, amnio for baby
Normal Trisomy 21
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