Zygote and Embryo formation Flashcards
What is a newly fertilized egg cell called?
A zygote
What is the zygote? (N? 2N?)
Diploid (2N) bc 2 sets of chromosomes are being joined together
What are the two types of fertilization? Which organisms do which?
Internal and external. (Internal-land animals, external sea animals)
How does external fertilization occur?
Gametes join together outside the body of the female
How does internal fertilization occur?
Gametes join inside the body of the female
How many eggs/zygotes does external fertilization make use of? Why?
Many/many
More likely to be damaged outside
How many eggs/zygotes does internal fertilization make use of? Why?
Few/few,
Protected by the moist internal environment of the female
What are chromosome mutations?
When changes occur (this is abnormal) and causing variation in the number of chromosomes (not 46)
What is a trisomy?
3 copies of a single chromosome (2n+1)
What does down syndrome result from?
Trisomy of chromosome 21 (47, 21+)
How common is down syndrome?
Average 3:1000 births, frequency increases w age of mother
What are characteristics of down syndrome?
Short, w small, round heads and other facial features, mental disabilities, with IQ seldom above 70, shorter life expectancy (more likely to have respiratory disease and heart defects)
What is Klinefelter syndrome?
Males with a trisomy of sex chromosomes (extra X chromosome)
How common is Klinefelter Syndrome?
1:500 male births
Characteristics of Klinefelter Syndrome?
Males, with male genitalia, but with underdeveloped testes that cannot produce sperm, and some female sexual development
What female sexual development is possible in Klinefelter Syndrome?
Enlargement of breasts, less facial hair, higher voice
What is a monosomy?
1 copy of a chromosome instead of two (2n-1)
What is Turner Syndrome?
Females, with female external genitalia, but have a monosomy of the sex chromosomes, only have one X-chromosome
How common is Turner syndrome?
1 to 3000 female births
What are symptoms of turner syndrome?
Female external genitalia but underdeveloped ovaries and other abnormalities, such as webbed neck, abnormally short, broad chest
What is parthenogenesis?
Development of an egg cell into a mature organism without being fertilized by sperm cell
Given example parthenogenesis
Production of male bees
What are the steps of normal embryo formation
Fertilization, cleavage, and gastrulation
What is cleavage in a zygote?
Zygote divides many times by mitosis, forming a hollow ball with a single layer of cells called a blastula
What is a blastula?
A hollow ball with a single layer of cells formed by multiple mitosis of zygote. There is no increase in size
What is gastrulation in a blastula
One side of the blastula becomes indented, forming a gastrula
What is a gastrula?
The product of gastrulation
What are the three layers of a gastrula called?
The outer layer is called ectoderm, inner layer is called endoderm, middle layer is called mesoderm
What is differentiation?
Cells of the three layers of the gastrula differentiate, or change into various tissues and organs of the animal
What is growth?
Increase in number and size of cells
What is fertilization?
Union of haploid sperm nucleus w haploid egg nucleus
