Transcript Chapter 27
Chapter 27 Human Genetics The Role of Chromosomes Chromosome Numbers in Living Things 1. Each human sperm or egg has 23 chromosomes. 2. Each human body cell has 23 pairs of chromosomes. 3. Different organisms have different numbers of chromosomes. 23 Chromosomes Sex Cells Chromosomes not paired Human Cells 46 Chromosomes Body Cells Chromosomes arranged in 23 pairs Chapter 27 Section 1 The Role of Chromosomes Detecting Genetic Disease • Genetic screening examines a person’s genetic makeup and potential risks of passing disorders to offspring. • Amniocentesis is a way of looking at the chromosomes of a fetus. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 1 The Role of Chromosomes • Doctors can also take a small piece of the placenta to obtain a sample of chromosomes. • The chromosomes are counted and studied to see whether parts are missing. • Karyotypes are charts where chromosomes are organized in pairs. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 1 The Role of Chromosomes Sex – A Genetic Trait • Sex Chromosomes and Autosomes – Sex chromosomes contain genes that determine an organism’s sex (gender). – The remaining chromosomes that are not directly involved in determining the sex of an individual are called autosomes. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 1 The Role of Chromosomes Sex – A Genetic Trait, continued • Sex Determination – In mammals, an individual carrying two X chromosomes is female. – An individual carrying an X and a Y chromosome is male. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 1 The Role of Chromosomes Karyotypes: Male and Female Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 1 The Role of Chromosomes Chapter 27 What are your chances of having male or female offspring? X XX Body Cell X X X X XX XX XY XY Eggs X XY Body Cell Y Y Sperm 1female:1male Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 1 The Role of Chromosomes Male or Female? Who determines the sex of the offspring? • The Father, because he donates the Y chromosome. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 2 Human Traits Survey on Human Traits Attached earlobes is a Recessive trait. Detached earlobes is a Dominant trait. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 2 Human Traits Survey on Human traits Being able to roll your Tongue is a dominant Trait. Not being able to roll your Tongue is a recessive trait. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 2 Human Traits Survey on Human traits Dominant Traits Free Earlobes Curly Hair Dimples Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 2 Human Traits Survey on Human traits Recessive Traits Attached Earlobes No Dimples Straight Hair Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 2 Human Traits Incomplete Dominance Some traits are neither totally dominant nor totally recessive. Incomplete dominance is when neither gene is totally dominant to the other. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 2 Human Traits Incomplete Dominance Snapdragons Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 2 Human Traits Incomplete Dominance • Sickle Cell Anemia • R = Round blood cells • R’ = Sickle Cells R R’ R RR RR’ R’ RR’ R’R’ Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 2 Human Traits Blood Types in Humans • There are four blood types in humans – A, B, AB and O. • A and B are dominant to O. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 2 Human Traits Genes on the X Chromosome • Sex-Linked Genes and Traits – Genes found on the X chromosome are X-linked genes. – A sex-linked trait is a trait whose gene is located on a sex chromosome. – Because males have only one X chromosome, a male who carries a recessive gene on the X chromosome will exhibit the sex-linked trait. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 27 Section 2 Human Traits Genes on the X Chromosome • • Color blindness is a problem in which red or green look like shades of gray or other colors. The gene is carried on the X chromosome and is a recessive trait. XC XC Y Xc XC XC XCXc XCY XcY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.