Transcript 14-1 notes
14–1 Human Heredity 14-1 Human Heredity Slide 1 of 43 Copyright Pearson Prentice Hall End Show Review • What is a chromosome? • What is one method geneticists use to predict the possible genotypes of the offspring from a specific cross? Slide 2 of 43 Copyright Pearson Prentice Hall End Show OBJECTIVES • Students describe how sex is determined. • Students know how to determine the genotypes of individuals using a pedigree diagram showing phenotypes. • Students know how to predict the probable mode of inheritance from a pedigree diagram showing phenotypes. Copyright Pearson Prentice Hall Slide 3 of 43 End Show 14–1 Human Heredity Human Chromosomes Human Chromosomes Cell biologists analyze chromosomes by looking at karyotypes. Cells are photographed during mitosis. Scientists then cut out the chromosomes from the photographs and group them together in pairs. A karyotype is a picture of chromosomes matched in pairs. Slide 4 of 43 Copyright Pearson Prentice Hall End Show 14–1 Human Heredity Human Chromosomes Human Karyotype Slide 5 of 43 Copyright Pearson Prentice Hall End Show 14–1 Human Heredity Human Chromosomes Two of the 46 human chromosomes are known as sex chromosomes, because they determine an individual's sex. • Females have two copies of an X chromosome. • Males have one X chromosome and one Y chromosome. The remaining 44 chromosomes are known as autosomal chromosomes, or autosomes. Slide 6 of 43 Copyright Pearson Prentice Hall End Show 14–1 Human Heredity Human Chromosomes How is sex determined? Slide 7 of 43 Copyright Pearson Prentice Hall End Show 14–1 Human Heredity Human Chromosomes All human egg cells carry a single X chromosome (23,X). Half of all sperm cells carry an X chromosome (23,X) and half carry a Y chromosome (23,Y). About half of the zygotes will be 46,XX (female) and half will be 46,XY (male). Slide 8 of 43 Copyright Pearson Prentice Hall End Show 14–1 Human Heredity Human Chromosomes Males and females are born in a roughly 50 : 50 ratio because of the way in which sex chromosomes segregate during meiosis. Slide 9 of 43 Copyright Pearson Prentice Hall End Show 14–1 Human Heredity Human Traits Human Traits In order to apply Mendelian genetics to humans, biologists must identify an inherited trait controlled by a single gene. They must establish that the trait is inherited and not the result of environmental influences. They have to study how the trait is passed from one generation to the next. Slide 10 of 43 Copyright Pearson Prentice Hall End Show 14–1 Human Heredity Human Traits Pedigree Charts A pedigree chart shows the relationships within a family. Genetic counselors analyze pedigree charts to infer the genotypes of family members. Slide 11 of 43 Copyright Pearson Prentice Hall End Show 14–1 Human Heredity Human Traits A circle A horizontal line represents A shaded circle or square connecting a male and a female. indicates thatrepresents a person a a female expresses the trait. marriage. A square A vertical line and a represents a male. bracket connect the parents to their children. A circle or square that is not shaded indicates that a person does not express the trait. Slide 12 of 43 Copyright Pearson Prentice Hall End Show 14–1 Human Heredity Human Traits Genes and the Environment Some obvious human traits are almost impossible to associate with single genes. Traits, such as the shape of your eyes or ears, are polygenic, meaning they are controlled by many genes. Many of your personal traits are only partly governed by genetics. Slide 13 of 43 Copyright Pearson Prentice Hall End Show 14–1 Human Heredity Human Genes Human Genes The human genome includes tens of thousands of genes. In 2003, the DNA sequence of the human genome was published. In a few cases, biologists were able to identify genes that directly control a single human trait such as blood type. Slide 14 of 43 Copyright Pearson Prentice Hall End Show 14–1 Human Heredity Mode of Inheritance • Recessive: disorders caused by having 2 recessive alleles • Dominant: disorders caused by having just 1 dominant allele • Sex Linked: disorders carried on one of the sex chromosomes (either X or Y) Slide 15 of 43 Copyright Pearson Prentice Hall End Show 14–1 Human Heredity Human Genes Recessive Alleles The presence of a normal, functioning gene is revealed only when an abnormal or nonfunctioning allele affects the phenotype. Many disorders are caused by autosomal recessive alleles. Slide 16 of 43 Copyright Pearson Prentice Hall End Show 14–1 Human Heredity Human Genes Slide 17 of 43 Copyright Pearson Prentice Hall End Show 14–1 Click to Launch: Continue to: - or - Slide 18 of 43 End Show Copyright Pearson Prentice Hall 14–1 A chromosome that is not a sex chromosome is know as a(an) a. autosome. b. karyotype. c. pedigree. d. chromatid. Slide 19 of 43 End Show Copyright Pearson Prentice Hall 14–1 Whether a human will be a male or a female is determined by which a. sex chromosome is in the egg cell. b. autosomes are in the egg cell. c. sex chromosome is in the sperm cell. d. autosomes are in the sperm cell. Slide 20 of 43 End Show Copyright Pearson Prentice Hall 14–1 Mendelian inheritance in humans is typically studied by a. making inferences from family pedigrees. b. carrying out carefully controlled crosses. c. observing the phenotypes of individual humans. d. observing inheritance patterns in other animals. Slide 21 of 43 End Show Copyright Pearson Prentice Hall END OF SECTION