Chapter 5: Sex Determination and Sex Chromosomes Susan Chabot Honors Genetics

Chapter Concepts Sexual reproduction, which greatly enhances genetic variation, requires a mechanism for sexual differentiation. Usually, specific genes on a single chromosome determine male-ness or female-ness during development. A variety of mutations can lead to sexual dimorphism (differences). In humans, the presence of extra X or Y chromosomes above the normal diploid number can be tolerated but will lead to distinctive phenotypes.

Chapter Concepts There is NOT a 1-to-1 ration of males to females at conception; the ratio tends to favor males at conception. Female mammals inherit 2 X-chromosomes at conception; the additional information in inactivated in early development. Temperature of incubation for reptilian eggs will determine the sex of offspring.

Heteromorphic Chromosomes: It is the GENES on the chromosomes that determine sex of the organism. MOST of these genes are on the sex chromosomes but some can be found on the autosomes. Introduction

Heteromorphic Chromosomes: characterize one sex or the other; XY pair in mammals. It is the GENES on the chromosomes that determine sex of the organism. MOST of these genes are on the sex chromosomes but some can be found on the autosomes. Introduction

Primary Sexual Differentiation: Secondary Sexual Differentiation: Vocabulary

Primary Sexual Differentiation: involves production and maturation of the gonads and gametes. Secondary Sexual Differentiation: involves overall appearance of the organism; non- reproductive organs Vocabulary

Unisexual/Dioecious/Gonohoric: Bisexual/Monoecious/Hermaphroditic: Intersex: Vocabulary

Unisexual/Dioecious/Gonochoric: organism that contains only male or only female reproductive organs. Bisexual/Monoecious/Hermaphroditic: organism that contains both male and female reproductive organs. These organisms can produce both eggs and sperm. Intersex: organisms of intermediate sexual condition; often sterile. Vocabulary

Human DIPLOID number is 46 ; HAPLOID number is 23. Remember, chromosomes are only visible during MITOSIS and MEIOSIS. Visualization of chromosomes during cell division will allow for the construction of a karyotype, seen below. The Y Chromosome Determines Maleness in Humans

47, XXY 1 in 600 male births! Result of nondisjunction during Meiosis. Tend to be tall, long arms, large hands and feet Outward appearance of male Undeveloped testes that fail to produce sperm. Female secondary sex characteristics are not suppressed; rounded hips, slight breast enlargement. Below average intelligence. Klinefelter Syndrome

45, X 1 in 2000 female births! Result of nondisjunction during Meiosis Short stature, skin flaps on back of neck, broad shield-like chest Outward appearance of female Undeveloped ovaries, may not produce eggs. Normal intelligence Turner Syndrome

Nondisjunction

47, XXX 1 in 1000 female births Would not realize the condition was present without a karyotype performed for confirmation. Normal primary and secondary sexual development. Rare cases of under-developed secondary sex characteristics, mental retardation. 47, XYY Above average height, below normal intelligence. Study done in 1960’s to show predisposition to criminal behavior due to this karyotype Other Conditions of 23 rd pair Nondisjunction