Download Chapter-14

Human Inheritance
Chapter 14
Biology Concepts and Applications, Eight Edition, by Starr, Evers, Starr. Brooks/Cole,
Cengage Learning 2011.
Human Chromosomes
 Human body cells have 23 pairs of homologous
chromosomes
• 22 pairs of autosomes
• 1 pair of sex chromosomes
Autosomes and Sex Chromosomes
 Paired autosomes
• Same in length and shape
• Have the same centromere location
• Carry the same genes along their length
 Sex chromosomes
• Identical in human females (XX)
• Nonidentical in human males (XY)
Sex Determination
 SRY gene on the Y chromosome
• Basis of male sex determination
• Expression initiates synthesis of testosterone
• Hormone causes embryo to develop into a male
 If an embryo has no Y chromosome (no SRY
gene), it develops into a female
Sex Determination Pattern
Sexual Development in Human Embryos
At seven weeks, appearance of
“uncommitted” duct system of
embryo
Y chromosome
present
Y chromosome
absent
At seven weeks, appearance of
structures that will give rise to
external genitalia
Y chromosome
present
Y chromosome
absent
10 weeks
10 weeks
ovary
penis
vaginal opening
uterus
penis
testis
vagina
birth approaching
Fig. 11.2, p.170
Autosomal Inheritance Patterns
 Some alleles on autosomes are inherited in
simple Mendelian patterns associated with
specific phenotypes
 Certain mutated forms of alleles give rise to
genetic abnormalities or genetic disorders
 Table 14.1 in Text for Examples
Autosomal Dominant Inheritance
Autosomal Recessive Inheritance
Key Concepts:
AUTOSOMAL INHERITANCE
 Many genes on autosomes are expressed in
Mendelian patterns of simple dominance
X-Linked Inheritance Patterns
 Certain dominant and recessive alleles on the X
chromosome are inherited in Mendelian patterns
 Mutated alleles on the X chromosome contribute
to more than 300 known genetic disorders
 Males can’t transmit recessive X-linked alleles to
sons (son receives X chromosome from mother)
X-Linked Inheritance Patterns
Hemophilia A  X-linked recessive
Interfere with blood clotting. Affect 1:7500 people.
Pedigree  chart showing the pattern of inheritance of
a trait through generations in a family
Green  Carriers
Red  Diseased
Fig. 11.8, p.174
Color Blindness
Key Concepts:
SEX-LINKED INHERITANCE
 Some traits are affected by genes on the X
chromosome
 Inheritance patterns of such traits differ in males
and females
Heritable Changes in
Chromosome Number
 Chromosome number of a parental cell can
change permanently
 Often caused by nondisjunction
• Failure of one or more pairs of duplicated
chromosomes to separate during meiosis
Nondisjunction in Meiosis
n+1
n+1
n-1
n-1
chromosome
alignments at
metaphase I
NONDISJUNCTION alignments at
AT ANAPHASE I metaphase II
anaphase II
CHROMOSOME
NUMBER IN
GAMETES
Stepped Art
Fig. 11-13, p.178
Aneuploidy
 Aneuploidy  Cells with too many or too few
copies of a particular chromosome
• In humans, the most common aneuploidy
(trisomy 21) causes Down syndrome
 Most other human autosomal aneuploids die
before birth
Aneuploidy:
Trisomy 21 (Down Syndrome)
Fig. 11.14, p.179
Polyploid
 Polyploid  having 3 or more of each type of
chromosome characteristic of the species
• Example: XXY (1:500 males)
• Klinefelter syndrome
• Example: XYY
Polyploid
 XXY (1:500 males)
• Klinefelter syndrome  Characteristics
• Overweight, tall, within normal range of intelligence
• Make more estrogen and less testosterone than normal
males
• Small testes and prostate glands, low sperm counts,
sparse facial and body hair, high-pitched voices, and
enlarged breast
• Testosterone injections during puberty can reverse
these traits
 XYY
• Normal OR May be taller with mild mental impairment
Animation: Autosomal dominant
inheritance
Animation: Autosomal recessive
inheritance
Animation: Human sex determination
Animation: Pedigree diagrams
Animation: X-linked inheritance