2d. Know new combinations of alleles may be generated in a zygote through the fusion of male & female gametes (fertilization)‏ 1

_____ + _____ = New Organism Once gametes are formed, the second half of sexual reproduction can take place. During ______________ a diploid organism is formed by 2 haploid parts. When a sperm is united w/ an egg, a __________ (fertilized egg) is formed which contains the combined genotypes of the parents to produce a new allele composition. 2

Fertilization The uniting of male and female ___________. 3

Zygote When a sperm fertilizes an egg Now a _________ cell 4

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2e. Know why approximately half of an individual’s DNA sequence comes from each parent. 6

2f. Know the role of chromosomes in determining an individual’s sex. 7

Copyright Pearson Prentice Hall Human Chromosomes Two of the ____ human chromosomes are known as _________ chromosomes, because they determine an individual's sex. Females have two copies of an ___ chromosome. Males have one __ chromosome and one ___ chromosome. The remaining ___ chromosomes are known as autosomal chromosomes, or ________________. Copyright Pearson Prentice Hall 8

Copyright Pearson Prentice Hall Human Chromosomes How is sex determined? All human _____ cells carry a single X chromosome (23,X). Half of all __________ cells carry an X chromosome (23,X) and half carry a Y chromosome (23,Y). About half of the _____________ will be 46,XX (female) and half will be 46,XY (male). Copyright Pearson Prentice Hall 9

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What are you? Females carry two X chromosomes ____. Males carry one X & one Y chromosome  _____. 11

How many chromosomes are in the cell? A normal human ___________ cell (every cell in the body except for the reproductive cells) contains 46 chromosomes. 44 chromosomes are homologous chromosomes (___________) 2 chromosomes are _______ chromosomes 12

Human Chromosomes Males and females are born in a roughly ___ : ____ ratio because of the way in which sex chromosomes segregate during _________. In humans, egg cells contain a single X chromosome. Sperm cells contain either one X chromosome or one Y chromosome. In a population, approximately half of the zygotes are XX (female) and half are XY (male). 13