Presentation on theme: "Human Genetics Review – What is a GENE? A gene is the unit that controls traits Genes are passed from parents to offspring Genes are located on our chromosomes."— Presentation transcript:
Review – What is a GENE? A gene is the unit that controls traits Genes are passed from parents to offspring Genes are located on our chromosomes
KARYOTYPE: A SET OF PHOTOGRAPHS OF CHROMOSOMES GROUPED IN ORDER OF PAIRS. Karyotypes are used to detect chromosomal disorders and to determine the sex of an unborn child
The 23 rd pair of chromosomes are the sex chromosomes which determine an individual’s sex. XX – Female or XY - Male The first 44 chromosomes (22 pairs) are called autosomes.
At least 1 (X) chromosome MUST be present for survival The presence OR absence of the (Y) chromosome determines sex of offspring
Normal Female Karyotype This karyotype would be labeled as: 46,XX
Normal Male Karyotype This karyotype would be labeled as: 46,XY
Chromosome Number Disorders Nondisjunction - Failure of chromosomes to separate during meiosis. –Abnormal offspring –Monosomy: one copy of a chromosome –Trisomy: three copies of a chromosome –Polyploidy: multiple copies of chromosomes
CHROMOSOMAL MUTATIONS Deletion- piece breaks off and is lost.
Duplication - piece breaks off and attaches to a homologous chromosome
Translocation - piece breaks off and attaches to non-homologous chromosome.
Inversion - piece breaks off and reattaches upside-down.
What are Sex-Linked Traits? Trait determined by a gene on a sex chromosome (usually X chromosome). Examples: Colorblindness, Hemophilia, Duchenne’s Muscular Dystrophy Females must receive 2 affected X’s in order to have the trait. Females with only 1 affected X are carriers. Males will always show a recessive trait located on the X chromosome because he only has 1 X.
Sex-Linked Disorders Genotypes for sex-linked traits are written using the X and Y chromosomes to show path of inheritance. C = normal vision c = colorblindness Colorblind male = X c Y Colorblind female = X c X c Carrier female = X C X c **Remember males CANNOT be carriers**
Sex-linked traits: Color blind father x carrier mother ? ? ?
Sex-Linked Punnett Squares In sex-linked traits, probabilities for male and female offspring must be calculated separately because traits are inherited differently.
Sex-Linked Punnett Square Practice 1.A colorblind female marries a man with normal vision. What is the probability of them having colorblind children? Key: ________________________________________ Cross: _______________________________________ Probability of having a colorblind daughter = ___________ Probability of having a colorblind son = ____________
Sex-Linked Punnett Square Practice 2. A genetics counselor interviews a couple with a family history of hemophilia to evaluate the possibility of having offspring with the disorder. The wife does not have hemophilia, but states that her father had the disorder. The husband is normal. Key: ________________________________________ Cross: _______________________________________ Probability of having a daughter with hemophilia = ___________ Probability of having a son with hemophilia = ____________
Predictions and People What is a Pedigree - chart that shows how a trait and the genes that control it are inherited within a family.
How to Read a Pedigree Circle = female Square = male Horizontal lines connect siblings or spouses Vertical lines connect parents and children Shaded figure = Individuals who are affected by the trait Non-shaded = individuals who are unaffected ***Carriers are half shaded*** **When illustrated in a pedigree, children are placed in birth order from left to right (Oldest to youngest).
What is a Carrier? - an individual who carries a recessive trait (heterozygous) that is not expressed and can pass on genetic disorders to offspring. Has normal phenotype
Practice The following pedigree shows the inheritance of a recessive trait. 1.How many generations are shown? 2.How many children did Parents of Generation 1 have? How many were boys? How many were girls? 3.How many children did Parents of Generation II have? How many were boys? How many were girls? 4.Use the key to determine the genotypes of each person in this pedigree. (Hint: label all homozygous recessives first) Key: R = Non-affected; r = affected
I Generation II Generation III Generation 12 3 4 5 6 78 9 10
Widow’s Peak is dominant over no widow’s peak W = dominant w = recessive Ww ww
Examples: PKU (an inability to break down the amino acid Phenylalanine (can cause mental retardation) Tay-Sachs (results in a nervous system breakdown and death) Many genetic disorders caused by AUTOSOMAL RECESSIVE GENES.
ALBINISM - a lack of pigment in hair, skin and eyes. CYSTIC FIBROSIS - caused by a recessive allele on chromosome #7 - causes excess mucous in lungs and digestive tract, increased susceptibility to infections.
Tay-Sachs Recessive Trait Disorder T = normal t = tay-sachs Tt ttTt TT Tt
Autosomal Dominant Disorders Dominant allele disorders are less common (typically a homozygous person (HH) dies therefore the trait can't carry on to offspring). Ex. Huntington Disease
Huntington’s Disease - dominance (H) a. No symptoms until 30’s or 40’s b. Nerve damage: loss of muscle control & mental function until death Hh hh Hhhh Affected Normal
Huntington’s Disease (dominant trait disorder) H = affected w/disease h = normal Hh hh Hh HH hh Hh
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