Download Chapter 14 Section 14_1 Human Chromosomes

5/11/15 CHAPTER 14: HUMAN HEREDITY 14.1 – Human Chromosomes
A. Karyotypes
B. Transmission of Human Traits
Mr. M. Varco Saint Joseph High School Karyotypes
•  A genome is the full set of genetic information that an organism carries in
its DNA.
•  To see human chromosomes, photographs of cells are taken during
mitosis, and later arranged in a picture known as a karyotype.
•  A karyotype shows the complete diploid set of chromosomes grouped
together, and arranged in order of decreasing size.
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•  A karyotype of a human cell contains 46 chromosomes, arranged in 23
pairs.
Karyotypes
Sex Chromosomes
•  Two of the 46 chromosomes in the human genome are known as sex
chromosomes, because they determine an individual’s sex.
•  Females have two copies of the X chromosome
•  Males have one X chromosome and one Y
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Sex Chromosomes
•  All human egg cells carry an X chromosome;
half of sperm cell carry X chromosome
•  More than 1200 genes are found on the
X chromosome; about 140 genes are
found on the Y chromosome.
Karyotypes
Autosomal Chromosomes
•  The remaining 44 human chromosomes are known as autosomes.
•  The complete human genome consists of 46 chromosomes, including
44 autosomes and 2 sex chromosomes.
•  Females: 46,XX
•  Males: 46,XY
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Dominant/Recessive Alleles
•  Many human traits follow a pattern of simple inheritance
•  The MC1R gene helps determine skin and hair color
•  Some of MC1R’s recessive alleles produce
red hair à an individual with red hair usually
has two recessive alleles
Transmission of Human Traits
Dominant/Recessive Alleles
•  Another trait that displays simple dominance is the Rhesus, or Rh blood
group.
•  The allele for Rh factor come in two forms: Rh+ and Rh•  An individual with both Rh+ and Rh- alleles would have Rh positive
blood.
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Codominant / Multiple Alleles
•  The alleles for many human genes display codominant inheritance.
•  One example is the ABO blood group, determined by a gene with 3
alleles: IA, IB, i
•  The alleles IA and IB are codominant, and produce molecules known as
antigens
Transmission of Human Traits
Codominant / Multiple Alleles
•  Individuals with alleles IA and IB produce both A and B antigens, making
their blood type AB.
•  Individuals with alleles IAIA or IAi produce only the A antigen, making their
blood type A.
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Codominant / Multiple Alleles
•  Those homozygous for the allele i (ii) produce no antigen and are said to
have blood type O.
Recap:
•  A person with AB-negative blood means that the individual has alleles
IA and IB for the ABO gene and two Rh- alleles from the Rh gene.
Transmission of Human Traits
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Sex-Linked Inheritance
•  A sex-linked gene is a gene located on a sex chromosome.
•  Genes on the Y chromosome are found only in males and are passed
directly from father to son.
•  Genes on the X chromosome have different consequences for males vs.
females.
Transmission of Human Traits
Sex-Linked Inheritance
•  Humans have three genes responsible for color vision, all located on the
X chromosome.
•  In males, a defective allele for any of these genes results in color-
blindness. In females, only 1 in 200 are colorblind.
•  In order for a recessive allele (ex: colorblindness)to be
expressed in females, there must be two copies –
one on each X chromosome.
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Colorblindness is an X-­‐linked recessive trait B= normal color vision b = colorblindness SCENARIO 1: Genotype for a male with normal color vision is XBY Genotype for a female heterozygous for normal color vision is XBXb SCENARIO 2: Genotype for a male with colorblindness is XbY Genotype for a female with colorblindness is XbXb 8