BIOLOGY · Stage 9 · Chapter 11: Human Genetics and Development
Biology 11.9 Chapter 11 Review: Human Genetics and Development
5 min read 4 parts Lesson 9 of 9
Lesson summary
11.9 Chapter 11 Review: Human Genetics and Development — Alhussan International Academy — Biology (Stages 7–9) notes: Revise reproduction, fertilisation, inheritance, fetal development and the effects of maternal lifestyle from Chapter 11.Gametes — testes make sperm and ovaries m…
- Amniotic fluid
- Umbilical cord
- Harmful substances
- Premature babies
- Breast milk
- Antenatal care
Section 1 of 4Reproduction and fertilisation
- Gametes
- testes make sperm and ovaries make eggs, each with 23 chromosomes.
- Sperm have tails and mitochondria and carry enzymes in the head.
- Eggs are large with a food store.
- Fertilisation
- it occurs in the oviduct when a sperm nucleus fuses with an egg nucleus to form a zygote with 46 chromosomes.
- Many thousands of sperm swim towards the egg, and the nucleus of only the successful sperm fuses with the egg nucleus.
- Embryo
- the zygote divides by mitosis, and the embryo implants in the uterus lining about a week later.
Section 2 of 4Genes and inheritance
- DNA
- chromosomes are long molecules of DNA, and genes are short sections that code for proteins.
- Alleles
- different versions of a gene.
- Offspring inherit one allele of each gene from each parent, so they show variation.
- Sex
- females are XX and males XY, and the sperm decides the sex, with equal chances of a boy or girl.
- Variation
- it comes from both genes and the environment.
- Identical twins have the same earlobe shape and blood group because these are genetic.
- Differences in height and body mass between identical twins are due to different environments, such as diet and exercise.
Section 3 of 4Development and birth
- Amniotic fluid
- it cushions the fetus and keeps the temperature steady.
- Placenta
- it exchanges oxygen, nutrients, carbon dioxide and urea by diffusion without mixing blood.
- Umbilical cord
- it carries blood between fetus and placenta.
- Birth
- labour begins with contractions of the uterus, the baby is born and the placenta follows.
Section 4 of 4Health of mother and baby
- Nutrition
- folic acid, iron, calcium and protein, together with antenatal care, give the baby the best start.
- Harmful substances
- smoking, alcohol and some drugs harm the fetus.
- Smoking reduces birth weight because carbon monoxide lowers oxygen supply.
- Drugs can cross the placenta, so doctors take extra care choosing medicines for a pregnant woman.
- Premature babies
- they are helped by incubators, ventilators, surfactant, feeding tubes and careful hygiene.
- Breast milk
- it contains antibodies.
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