\nWhen the males produce two types of gametes, such a male is called heterogametic male. Following conditions will explain the mechanism:
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a. XX-XY Condition:
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In man, there are two types of sex chromosomes X and Y. The female has a pair of X chromosomes and is expressed as XX, while the male is expressed as XY. The X and the Y chromosomes in males act as homologous chromosomes during meiosis and pass into different gametes. Thus, males produce two types of gametes and are described as heterogametic while the female, which produces only one type of gamete, is homogametic.
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b. XX-XO Condition:
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In insects, such as cockroaches and some roundworms, the Y chromosome is missing in males and is expressed as XO, while the female is XX.
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B. Heterogametic Females: \nWhen the female produces two types of gametes, such a female is called heterogametic female.
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a. ZW-ZZ Condition:
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In vertebrates, such as fishes, reptiles and birds, the female has heteromorphic sex chromosomes and males have homomorphic. They are represented as ZW and ZZ, respectively.
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b. ZO-ZZ Condition:
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In some butterflies and moths, the W chromosome is lacking and the female is ZO and the male is ZZ.
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C. Haplodiploidy: \nHaplodiploidy is a condition seen in honeybees, wasps, ants and termites. The female is diploid, while the male is haploid. The diploid female is formed by the fusion of the sperm and egg, while the male is formed directly from the egg by the process of parthenogenesis.
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D. Genic Balance Theory of Sex-Determination:
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Bridges' Genie balance theory for sex determination in Drosophila, states that chromosomes are the carriers of genes for femaleness and autosomes are the carriers of genes for maleness. According to this theory, sex is determined by the ratio of the X chromosomes and autosomes.
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E. Environmental Determination of Sex:
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In some animals, environmental cues play an important role in the determination of sex.
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a. The larva of Bonellia, a marine worm develops into a female, if it settles down alone. A larva coming in contact with the already grown female, changes into male and lives as a parasite in the uterus of the female. \nb. In crocodiles, low temperature induces femaleness and high-temperature maleness. \nc. In turtles, temperature below induce maleness and above femaleness.
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Odisha Board Solutions for Exercise 1: SAMPLE QUESTIONS
Author:Odisha Board
Odisha Board Biology Solutions for Exercise - Odisha Board Solutions for Exercise 1: SAMPLE QUESTIONS
Attempt the free practice questions from Exercise 1: SAMPLE QUESTIONS with hints and solutions to strengthen your understanding. Bureau's Higher Secondary Biology Class 12 solutions are prepared by Experienced Embibe Experts.
Questions from Odisha Board Solutions for Exercise 1: SAMPLE QUESTIONS with Hints & Solutions