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

Fig. 11.2, p.170 At seven weeks, appearance of structures that will give rise to external genitalia At seven weeks, appearance of “uncommitted” duct system of embryo Y chromosome present Y chromosome absent Y chromosome present Y chromosome absent penis 10 weeks vaginal opening birth approaching uterus ovary testis penis vagina

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 Pedigree  chart showing the pattern of inheritance of a trait through generations in a family Interfere with blood clotting. Affect 1:7500 people.

Fig. 11.8, p.174 Green  Carriers Red  Diseased

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

chromosome alignments at metaphase I NONDISJUNCTION AT ANAPHASE I alignments at metaphase II anaphase II n + 1 n - 1 CHROMOSOME NUMBER IN GAMETES Stepped Art Fig , 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 , 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