Transcript 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